Me personally I hold a Libertarian view on the age of majority in America. If you're old enough to buy porn, be allowed to drive, kill some towelheads overseas with an M16, and vote for your representatives then I think to me you are also old enough to drink and smoke but that's just me.
That's just how I view it but even then I still don't think kids should be put on hormone therapy and chop their nuts off until they reach the age of majority to make an adult decision like this just like everyone else in the country anyway.
Whatever you do as an adult is up to you because your parents cannot make every decision for you when you become a legal adult. Whatever kids do it's the responsibility of a parent to make sure their kids aren't making the wrong choices that will affect them later on; just look at the bastards that end up in Juvenile Hall or become homeless because their parents were too incompetent to raise them right by that point.
I've known kids when I was growing up that wanted to "become a gangster" or "become a Cholo" and even did drugs and shit and they ruined their lives because they were young and impressionable and their parents didn't gave a shit anyway.