A couple of small points I'd like to address:

Yes, it's true that in many cases artists do tend the make the bodies of their female subjects rather willowly or pixiesh if you prefer with some of the differances in body you mentioned.  These tend to be alittle bit more variable from artist to artist however (in my exprience) and it's hard to cover a whole field in one or two posts, heh. 

It's additionally intresting to note that as many western artists started to do their own anime characters, there personal styles often varied very wildly from the norm, particullarly in cases of body type.

I would also agree with you, to an extent, that breast size is not a typical determining factor in a character's age.  I would point out, however, that basic development throughout the body, is used, which naturally enough includes breasts to show a person's level of maturity to an extent.  What I mean is that obviously a pre-pubescent character is not going to be showing any signs of sexual development.  Often additionally very young characters will (although not always) have some characteristics in line with the "chiby" style characters such as rather short and stubby extremeties like arms, legs, feet, hands, etc, very small torsoe and heads that while  will look somewhat exaggerated in comparison because of the disportionate size of their bodies.

This is part of why often more mature characters tend to take on some of the attributes you mentioned, such as somewhat longer limbs in comparison to a realistic character, and the somewhat smaller then normal torsoe regions are tyically a side effect of this keeping growth in porpotion (I know that's alittle hard to follow). 

As to the school uniform thing, this is often somewhat confusing if you're not familiar with the fact that traditionally school uniforms were standard not only thoughout highschool but into college as well.  Nowfrom what I understand this has changed somewhat, at least at the college level, but many older artists still call on their own expriences during their school years (which is understandible) in doing their art. 

As a result, many animes that take place with colleges as the primary setting for their characters will show the students in some form of uniform, and typically the only real varations between that and a uniform from for example highschool will be in terms of school logo and or color.

This is also the case with grammer school age children were often the uniform varation for boys is short pants or trousers and a collored shirt, and for girls a skirt and blouse of the same colors, and also for very small children who are usually dibicted in a sort of unisex smock, short pants or skirt depending on sex, and even a rather odd addition in the form of a sort (as it looks to me anyways) cross between a boonie hat and a pith helmet sort of headgear.

To give an example of the differences one sometimes can encounter between eastern and western cultures, a friend of mine who lives in the east once did a anime style picture of me based on my discription of my daily life (I was still in high school at the time) here in the west.  I was quite suprised when the picture had me dressed in what he imagioned someone in the west would wear on a day in school, namely a complete school uniform (and rather a cute one at that.. heh).  The whole thing was rather sweet in a way and I didn't have the heart to correct him, but the point is where as those of us in the West tend to associate school uniforms with things like private and or religous schools, or in some cases public schools that are so concerned with peer violence in relation to clothese they've started using the uniform principle, in traditional eastern culture (and as a by product anime culture) the school uniform principle is a fairly universal one.

There is a great deal of symbolism in traditional Anime that is often lost to the Western viewer owing to culteral differences.  I could start rolling off examples (the symbolism associated with colors alone is staggering) but I won't.  I mention it however because once again artists who are steeped in the anime style mindset sometimes need to step back a bit and remind themselves that alot of people who are less familiar are not neccessarilly going to get where they are coming from.

As too the suggestion that perhaps extreme bust sizes would help to more clearly establish different A3 characters as being more obviously adult, I'll grant that it's (sadly) not without some precedent.  There are a number of artists who have done all sorts of body varations with different exaggerated characteristics to give their characters a unique feel, often I think to try and set themselves apart from the traditional anime artist.  Exaggerated breast size is certianly one varation that's been done.  There are also things like overall body shape, I've seen a number of artists try to give their characters a more Westernized feel with more realisticly proportional body and sometimes head structure for example.  There are certianly plently of Morphs to turn A3 into anything from a large amazon, to a giganticly obese person, to a overly endowed and exaggerated female form, and even into a male version of herself.

I would point out, however, that in traditional anime such exaggerated forms were typically given to a character in order to convey a sense of differance or gross exaggeration, and that if such differences were to become the norm, it would kind of defeat the purpose.  It's rather like suggesting simply using the realistic morph for Aiko or Hiro.  Yes, then obiviously it's going to be more easy to establish something like age, but it's not going to be an Anime character, it's going to be a realistic character like V3 or M3, which again I think would kinda defeat the purpose since it would not be anime art.

The other idea I've heard tossed around a bit is simply to complety ban any A3 nudity.  I honestly don't think this is going to really help in the end.  For one thing, while A3 may be one of the more popular Anime characters to use in renders, she is certianlly not the only one out there.  I myself have a number of different anime characters in my runtime that if I were inclinded towards doing nude anime style renders could certianly fill the gap very well.  In addition to that I see alot of artists starting to tag any images they do of Aiko in a compartivly skimpy outfit as containing nudity, even though really they don't, so I'd hate to think all those images would suddenly be pulled as well and that the next step would most likely be people screaming back and forth as to at what level of attire A3 begins to drift into a potential "nudity" catagory.

Similarly it occured to me to suggest creating a list of morphs that can and cannot be used with A3 if she's going to appear nude with a accompanying list for Hiro and or any other anime characters.  But you see, many artists who've designed characters use degrees and varations on morphs that at first glance would seem obivious to me as being no-nos to create characters that are quite obviously adult.  So I don't think outlawing certian morphs is really going to work well either.

Somebody (jokingly as I recall) also suggested making A3 have a old or wrinkled face in all nude renders.   While I don't think it needs to be taken to that extreme, of course, I think this is one possiblity (here me out please).  I mentioned before that there is that grey area in anime in regard to peoples ages from about the mid-teens to mid-twenties.  However, there are quite a number of characters that are made to be obviously older adult characters in the anime field without being extremly old aged. 

Okay right about now the "But I want them younger (but adult), and pretty, and naked" crowd is probably readying the tar and feathers for me, but just hold on a second before you put the noose around my neck.

What I'm talking about would be a varation if you will on the already put forth "big breast theory" lol.  Okay, let's talk seriously.  To begin with if A3 is going to be either nude or next to nude in your renders, you probably don't have to worry alot about clothing fittings, so I'm going to suggest some of the standard anime techniques I can think of off the top of my head to ephesize an adult image for A3, while still keeping her compartivily pretty and also Anime in nature.

-Leg length.  Alot of the boys out there seem to like a good pair of long and sexy legs on a girl, so lets increase A3's height, but put alot of it into the legs.  You might also want to lengthen the torsoe a bit, so it doesan't cross into ridiculous but lets tag on a few inches in height to the legs.  Heels can also work wonders (and I think not detract from the general nude principle you're going for).

-Accompanying arm length and also neck length.  Let's get those going a bit too, partially for proportion but also because a nice gracefull neck and delicate willowy arms are generally considered good features on most women, and I think that's what we're shooting for, cute or pretty or sexy but in a adult way.

-Hips, buttocks, breasts, and waist.  Now again, I don't think we need to get to extreme on any of those, but play around a bit, let's give our grown up A3 a nice shapely figure that emphesizes a fully feminine and adult image without getting so disproportionate she looks like she's going to take a step and fall flat on her face from her poor breasts being bigger then her head (although I'm sure some folks would quite enjoy that lol).  In general when in doubt fall back on working those attributes towards the typical sociatial ideals, IE slime waist, shapely hips and buttocks, and breasts that while not neccesarilly huge are certianly fully developed (I'm sure you guys will figure out something, ha, ha I'm having way to much fun with this).

-Feet and hands.  I think you can mostly leave those alone, I say this because alot of folks are inclined to put some form of footwear on even their nude or barely there outfited A3s and so it's probably best to leave them largely in there orginal form provided they don't look dispropotionate.  One of the commen associations with women is smaller hands and feet then they're male conterparts anyways so I don't think that's going to effect the underage issue much.

-Tone and muscularity.  Once again you don't neccesarilly have to go to any extremes here, but alittle tone and muscle can both increase appeal and create a more realistic figure.  Most modern women indulge in some form of excercise and it adds a bit of age I think all in itself because it speaks to life-experience.  No we're not talking "amazon" proportions here, but concentate on some tone to things like legs for example, or the abs or gluts.  Let's keep our Adult A3's healthy and happy.

• Face.  Okay now we come to the big one.  But it's not as itimidating as one might expect.  Take a look at some of the pre-existing face morphs and character packs for A3, the Kleo ones are some of my favorites and they're free.  There's alot of varation there to get across a character image that's going to be mature but still beautifull and viberant.  Let's see... Cheekbones and narrowing the face a bit to give it a somewhat less rounded look, nothing to extreme but those two are some good areas to work on I think to deephize the kind or rounded anime head without neccessarilly going to far.  Make up varations using different textures is real important.  You don't have to cake it on, far from it in fact, but try to find a combination that is going to ephesize artfull application and experience.  I'd generally stay away from colors like pink for example which tends to give a more girlish appearance.  In general I suppose either proffesional and/or pretty but with a proffesional edge to it that speaks to years of practice.  Take some time with it, it really is one of the tools I've seen used in characterization for anime that can help emphesize a characters role or age for that matter.  Oh and expression, that can make quite a differance as well and and a nice alternative if you don't want to add to many age lines or anything to her.

-Hair.  Along with make up, this is often a key factor in giving a character (particullarly if they're going to be nude and not have clothing style to fall back on) a older more mature apperance.  Unfortionatly the paradox is there are no real absulutes here.  Depending on what you want your character to be and or express, and what other factors you've already used, is naturally going to play a big role in your choice.  For the purposes of age, I'd say in general (although this is by no means absulute) I would stay away from the "cute" hair styles like pixish styles, pig tails, twin buns, etc.  Maybe go with something really long and rich for a more beautifull character, or short or pulled back into a simple bun or braid for a mor professional look, but really those are just some kinda typicals off the top of my head.  I'm sorry if I'm being kinda vague but it's such a primary form of individual expression.  Go with what looks right for a character but recognize that if you go with a style generally associated with younger women it might end up a bit of a handicap in establishing age.

Kay's I think that's it for the moment except that props and setting can also play a role sometimes. 

One other thought.  At some of the forums I've been on, they went ahead and established a specific thread where every time anyone was warned or banned there was a short public announcement to that effect, stating the reasons why.  For example:  "Crimson Desire has been banned from the site for three months for repeated violations of the TOS as pertaining to posting images containing underage nudity"  Or words to that effect.  

This did a couple of things.  First it established a publicly viewable history in this case one would only have to look back a bit in the thread to find entries for previous violations, example "Crimson Desire has been given a warning for posting a image containing underage nudity and the image has been removed" followed by, "Crimson Desire has been given a second warning for posting an image containing underage nudity and the image has been removed the artist has been informed that one mor violation will result in a ban of three months" etc. 

In addition, members were allowed, withen reason, to post there opinions on the matter, provided they were civil and respectfull about it.  Of course there are good and bad points to this approach I'm not going to go into now because I'm tired and I think I've dragged this out long enough but I'm sure others will and it' s a thought is all.

Kay, I'm done babbling for now.