It has been shown that a face with more child-like features is considered "more attractive" than those that have less 'child" features.

http://translate.google.com/translate?prev=/language_tools&u=http://www.beautycheck.de/

Given that you can see that many vendors and freebie providers subscribe to that line of thinking and as a consequence there are blurred areas where age is concerned.

So far as images in the gallery go, unless they are actual photographs of real human beings, there is no way to "prove" the age of the subject in the image.  Because of that, the moderators have to use what is available to them, visual means, in order to determine age. And that is not always easy to do because it's highly subjective. What I might consider a child could look to be an adult to someone else, and vice versa.

The determining factor for age is most often decided based on the face.  A character could have size 99 ZZZZ sized boobs, but if the face looks under 18 years of age (IE: has a lot of child features), that character is considered a child and the image is removed. Those decisions aren't made arbitrarily. The image is discussed and the staff give their opinion as to age and the decision made based on the majority.

So far as Kate Moss. Yes, she is of age and can strip and pose if she wants, even in this gallery if Renderosity could prove that she is who she says she is and that her consent form is legit.

However if she were just a 3D character and was  purely fictional, there would be no "age" and again, the determination would have to be made based on purely visual means. And because Kate has a great deal of child like features, which is what makes her appealing to look at, the image would more than likely be considered "child" and removed from the gallery.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi