Granted, I skimmed (no milk pun there) the responses so far, but I do feel I can voice an opinion here.
The teen-pages and whatnot don't necessarily do it for me, though some barely-18/19/21-claiming women who don't look like children definitely do something for me. I guess for me it's all in context. If it appears that someone legal is doing something of their own volition (and we dont need to start on the pressures of the sex trade or gender-roles in a patriarchical society), there's all the more attraction.
Secondly, I find it interesting that women used to be sexual objects at 15, 16, 17, and 18 a hundred years ago (and further back), as partners, mothers, etc. And with the advent of "women's liberation" and the associated desire to compete equally with males of the world - career, education, etc - meant that women weren't seen in that light until they were well into their 20s, and now that same liberation, coupled with changing societal norms and new gender roles means the sexualisation of "teens" at younger and younger ages once again. What do people make of this?
Sorry for the oft-derailing train of thought. Feel free to poke holes in my stream of consciousness; I don't claim infallibility.
That said, I have an aside which I think is on topic, as others have mentioned diet, urbanisation, and lifestyle. While travelling in Scotland a few years ago, it seemed to me that UK women (generalisation!) seemed to show the more physical signs of womanhood (hips, breasts) at earlier ages than in North America. Anyone out there have a view on this? I wasn't sure if I should attribute it to diet, considering the horribly fattening diet in North America, but there was little else I could go on.
Wow. long post. sorry