I've written NC-17 of two of the characters who were 14 and 17 for this fandom. And yeah, in some states, they're underage. But they're teenagers. Teenagers have sex. Some of them wait until they're legal, some of them get too curious before that. Deal with it.

It sounds to me like you're just bothered by the idea of kids having sex more than anything else. I've seen far, far worse stuff in other fandoms.