aging...why isn't it happening internally?

I was online chatting to a friend yesterday and we realised our 10 yr high school reunions are coming up...but we both still feel like kids! I mean, at least in the last year I have stopped being mistaken for a 16 year old, so something must be happening physically, but mentally, adult things still awe/bore me and I still fight (and often lose) the urge to put my foot out and tap the lever to lower other people's computer chairs during meetings, hide in the bushes and jump out at friends walking past and buy myself lollies in the supermarket.
That is one great thing about my age down on paper at least - I can now buy whatever and drive myself wherever I want...