I think it's hard to assess given the behaviors of the Ponies are so much more evolved than typical human interaction. That said, they're still maturing through normal emotional development. So you've got a situation that you can't really compare against in real life (at least anywhere I've ever seen.)
Anyways, don't we all know some 18 year-olds who act as mature as 40-year-olds, and some 40-year-olds who act as immature as 18-year-olds?
http://www.votable.com/tv-show/my-little-pony-friendship-is-magic