Sup brother, I'm also 19. I started out on a gsxr 600 (brand new, laugh all you want ) but that's just me. I rode my friends 125, let me tell you, it's fun as hell but you will get bored of it soon... Now I got my zx6r and let me tell you son, once you get on the 600's you'll feel untouchable..
And once you get on the 1000's you'll feel 600's are small bikes