I empathise with all of these feelings! It doesn't get any easier with age either (I'm 24, and feel practically ancient) I think these feelings are routed in societies obsession with youth. The masses praise anyone who's successful, talented and young, more so than their older contemporaries. (just look at child prodigies).
Enjoy being 19! :)
RE: Alive& kicking: You're not old, you're just lying to yourself