The age of consent varies from country to country. In the United States, it also varies from state to state. In some countries, the age of consent for heterosexual activities is different than for homosexual activities (no really, that happens).
To avoid any legal hassles for myself the rules for sexual activity for teenagers is as follows:
1. There is to be absolutely no sexual contact between adults (let’s say 20+) and anyone under the age of 18. Yes, these numbers are higher than most areas require but we’re going to go with the law of averages.
2. Two teenagers above sixteen can get their freak on — I don’t care.
3. Child molestation or rape can be discussed but not depicted. PERIOD. You must also warn for such discussions in your author notes.
I don’t care what your “plot” needs, what the canon of your fandom requires OR does for that matter. These are the rules of Rough Trade. You can follow them or just simply not participate. OR you can skip the sex in your rough draft.