Experimented with a flat chested girl when we were 15. Still cant get enough of flat chests after that. Got into rough sex (Anal, DP, ATM) in my early twenties when I had nothing better to do than watch porn at home. Got into trans girls and femboys a couple years later even though I could not stand anything of the sort before. It was a domination and power thing at first like sissification but now I can appreciate just a really pretty girl with a dick too.
That's an interesting question. Now I think about it it was almost all before 16, becoming slightly more open minded as I have gotten older - but it was mostly set way back then.