personally, i don't think it's just a matter of "personal" opinion, it's a matter of consistency.  aiko, anime doll, belbel, mizuho, yuki, and other custom figures and morphs are anime.  many anime characters that look just like them facially and body-wise are declaratively older than 18.  for instance, in the ranma series, kasumi (19) had basically the same face as her sister, the female lead akane (16).   akane had a shorter body, more rounded limbs, and less of a chest.  that is, her body declared her age, not her face.  now, if you want to decide that anime (which is interestingly a stylistic decendant of disney) is always underage, then great, go ahead.  that's simply not what the genre itself says.  nor how anything in anime works.  if the female (or male for that matter) isn't a particularly elderly character, she gets pretty much the same facial treatment- whether she's a bio-engineered spy working for the government or a school girl with awakening powers, or even a young child.  if you notice, yamato's chibi belbel (see daz forums) has a different body, but not a different head.   that's anime.   we're not talking about putting taking a child figure with child's face and hips, adding a breast morph, and just declaring the person above age.  anime is a specific stylistic genre, and in the rules of anime, i'd say aiko is an adult character. looking at the younger anime characters, i'd actually say she looks way too old to be a child.

now if you want to go and declare all anime with nudity child porn (and there's a lot of non-hentai anime with nudity), go ahead.  but that's neither the intent nor the perceived intention among its fans.   you might just as easily say that hiro is a  female child character, since his face has only minor differences (as is true of most males in anime).