I do seriously have to wonder what inspires people to think they are "too old for...."
Is it a member of the opposite sex who looks down on it?
Peer pressure?
The way they were raised?
????
I mean, when you get right down to it, how is ANY form of entertainment more or less mature than anything else. Somebody a couple posts up mentioned motorbikes - for example, I find *that* hobby childish. I mean, you can get HURT! For teenagers (17,18,19)? Sure. But, c'mon, riding a motorbike after 24 just screams 'midlife crisis'.
At least, that's one opinion. I'm sure a case could be made for anything.
The number of 'entertainment' options that are really, REALLY clearly childish are pretty few and far between, IMHO. And almost everything has a more mature side to it - even playing games. Play more adult games! Play in teams where you have to cooperate, plan things out, and work together. Etc - do things in a more adult way!
(In any case, my preferred format of gaming is pen-and-paper wargames, and you'll never get me to believe that anyone is too old for THAT! Hell, I've confused more than a few hobby shop owners when I asked about wargames. Seems nobody under 60 or so plays them. Or, almost nobody.)