Well 1st, you've got to get in the context, so they are wolves, and wolves don't live as long as we do, so they grow up fast, and at the beginning of the movie the are teens (hence Kate needs to go to alpha school) and they look younger at the end than they do at the beginning plus the song was called "teen love" or something like that. By the end (after Kate finishes alpha school) I would have to say that she is like an adult (but more like that transition to adult from teen, so not that much of an adult), in relative to human years
well the title of the song played at the beginning of the movie is called pre-teen wolf. So towards the end of the movie they are old-teens (18-19 years old). In the deleted scenes I say they are about 23-27 years old.
