I've been with Nintendo since the NES. I'm 21.
(Also, I think a thread like this has been done before).
In my experience, only people who prefer Sony or Microsoft say that Nintendo is childish. Non-gamers don't really comment. So in the end, whoever says "Wii is childish" is biased anyway. But then, it doesn't really matter what anyone else thinks about us, we like what we like.