I'm wondering what some good H anime/manga series/authors have good stuff with girls who are petite, relatively flat, etc., but who are past the legal age. 13 is ok (that's the official age of consent in Japan), but preferably a little older; only really big thing is that she's small and flat. A legal DFC. Judge it like letter grades: AA is best, A is just as good, B's still good so long as it's stable, and C is borderline.
One thing particular is no major fluctuations in size (I've seen manga where a girl's an A cup in one frame, an E in the next, and then a B in the third).

A great example of the sort of thing I'm talking about is Hanamizawa Q-taro. Most of his girls are high school or above, and very few have any need for bras.