If it's a university setting, that's very possible. I've known first years who were in their late-fifties IRL. It's just socially acceptable now for kids to go to university right after high school, because of stuff such as government loans, but apparently, if we go by Rinnee's post, such loans aren't possible, or are rare.

And just because it's thought up by Americans doesn't mean that the legal drinking age would be 21. Fictional settings don't have much to do with where the author was born/raised/located. Anyways, what's posted is posted. If it wasn't that way, I'm pretty certain someone would have stopped Lupus from mixing explosive dust. XD