Well, I was going to say the NES version (only one I've played so far) gave me the impression they're young teens, or possibly start out as children but grow a few years in the course of the game (just that it's not made obvious like doing a time skip or anything). I wouldn't expect 10 year olds to save the world or to have the love story that seemed to be hinted at with that princess, but we know they're not adults and they do kind of "act young" compared to say a 16-18 year old.

So yeah, 14 sounds right