HK, when I was 15 and a freshman in high school, my boyfriend was 19 and a Ph.D. candidate, and we were sneaking around having sex without my parents' knowledge. (They knew about the boyfriend, just not about the sex.) For better or for worse, girls (or boys, but I think girls are more at risk) can end up "accelerated" socially as well as intellectually. I have no advice for you, but plenty of sympathy.

The funny part is that the relationship died a natural death as I realized that he wasn't really as mature as I was.