23 going to 24 next May.
Many have said it before, so I'll say it again. Personally, I don't care about the ponies. Don't feel like watching the cartoon, but I won't tell people not to mention/talk about something they like (or turning them into funny memes). Like any media, if you don't like it, don't watch it/read it, but don't deny other people of doing that, or you just might find yourself as a intolerant person.
I have no idea what my mental age might be (I hope it's higher than it seems to me), but I believe it's better to have some level of immaturity through life, than to be an old, annoying and fun-draining person, living in the past and damned forever to not accept new things, or at least learn to live with them.
Also, OP, why don't you tell us your age, too?