That... probably depends on who's caring about it, I think? And sometimes the laws involved, too -- there's places in the US that will recognize ages of the majority below their own on certain subjects and to certain extents, if whatever it's relevant to happened outside their jurisdiction and somewhere where the age was lower, ferex. More or less like MSH is saying, though -- the rub would be if the parents or the citizenship country are trying for some kind of legal challenge and actually have some way to make the host country listen to them. International jurisdiction stuff basically defaults to bloody complicated and gets worse from there. Best bet to find out would probably be to contact (email, whatever) an organization that deals with international stuff involving minors (US, ferex, would be something like
these guys). Bit of googling couldn't find any relevant information, unfortunately.
And it would depend, MSH. Theoretically for US citizens the US age of majority applicable to them applies
everywhere so far as being charged in a US court goes, because our laws follow all of us everywhere and if we do something illegal by US laws but not the local ones, we can still be charged when we get home (possibly via extradition due to the legal issue in question) and tried in a US court. It pretty close to never sodding
happens vis a vis majority laws, so far as I'm aware, especially for cases that don't involve stuff like sex tourism (particularly because a lot of the stuff relevant doesn't actually penalize the minor, but instead whoever did whatever -- sold beer, screwed, juggled flaming minigun chainsaws, who the hell knows -- with them), but it's a possibility. I'm not entirely sure how many countries have similar legal mechanics going on, but last I remember paying anything attention I seem to recall the answer being "most of them".