It all depends how old you feel and act I guess.
I'm 27. I don't realy feel too old for anime.
I guess it has to do with how we grew up too - I'll likely still be watching anime in 10 years. I don't know of too many 37 year olds who watch anime now, then again, they didn't grow up with it.
Some animes just have a certain nostalgia factor to it, and I think it's quite normal you like now what you liked when you grew up. Sure, there are some things you can grow out of, but if you had so much fun watching anime as a kid, why stop now?
Some anime can be all serious and emotional like Clannad, not all anime is immature. Try making a 10 year old watch Steins;Gate, see if they even grasp what the hell is going on.
I get your drift though, I mean, I'm ALREADY 27, at least that's how I feel. But I have no intention of letting my inner child go away yet
