Alle Kunst ist der Freude gewidmet

I've always thought that if someone's old enough to go out into the world on their own and somehow make a living for themselves, they're old enough to be considered an adult in most aspects, regardless of how young or old they are. Of course, there's definite squicks regarding certain things, but based on general trends, anywhere from 15-16 seems to be a good ballpark for FE-land.