Hah,

Although I'm a little younger (21), I too feel like my development is a little retarded. I only got my driver's license recently, I have minimal work experience; little things that seem so basic have somehow escaped me, like the proper way to tie your shoes or basic math skills most people seem to grasp (like cross multiplication). I play a lot of games but I never get good at them, and although I write well I have enormous trouble writing. I'm fairly intelligent, yet I feel like a dumbass a lot of the time.

Don't even talk about social relationships.

Don't get self-discouraged though, everybody eventually gets it at their own pace, it doesn't matter how brilliant or idiotic you are.