I'm 21 and I collect Monster High dolls to make custom dolls, I play with ball jointed dolls, I collect pokemon cards and play the video games religiously, anything Hello Kitty is MINE, and for Christmas 2010 the only thing on my wishlist was "a buttload of Nerf guns" (which I did get. hahaha).
I don't feel bad about acting like a kid right now. When I was younger, my parents didn't have the money to buy me the things I wanted. Now that I'm older, I make my own money and can buy my own toys! Bwahaha!
Just because you like toys doesn't automatically mean you're immature, so don't worry so much about it. I still carry on with a job (well, not at the moment because apparently no one wants to hire anyone around here), I pay my bills, I cook my food, I ride the train/bus quietly like a well-adjusted adult, etc.
There's no shame in having a childish side, in my opinion.