I've changed my reasons since then, but I think I got into fitness because I was bored. I think I started working out (well, beyond what we were forced to do in PhysEd. classes) when I was 19.
My first were The Firm Vol. 2 and a kickboxing one called Kickbutt.
The first workout tape that I actually stuck with, though, was Leslie Sansone's 2 mile walk. :-)