I'm 39-going-on the big 40(sigh). I neither feel like it or act like it. Actually, at work, a guy about half my age asked me(all condescendingly) what my age was. I told him and he sneered, since I and another co-worker were goofing around having a good time.
I forget where I read it, but recently, I ran across an item that I'd seen before that said something to the effect that children laugh, like 150 times a day(or so), and adults laugh,like, 7. I'm somewhere in the middle, probably alot closer to the children's average than the adult's. If that makes me immature, oh well....
Postscript--That guy at work is a big stinky poopy-butt.