How old is Belle?

And I don't mean Belle from Once Upon A Time; I'm talking about our brunette bookish babe in the gold dress! I mean, we know that the Beast/Adam is 21 의해 the end because it says so in the film - when taken into account that most DPs fall in between ages 14-20, we assume that Belle is either 21 또는 a little bit younger. What does everyone else think?