I initially got in to hair metal bands because of Headbangers Ball on MTV. Then in 8th grade a friend of mine and I dared each other to get a random tape (it doensn't seem like much of a dare, but $10 - $15 is a lot of money to part with when you are a jobless 8th grader). I ended up getting Exodus' "Pleasures of the Flesh" and was instantly hooked on thrash metal buying everything I could.
Once in college I got away from metal (I couldn't get in to the death metal direction because I found the singing annoying) and got in to grunge, punk, trip hop, and some strains of progressive or avant rock and listened to that for a while.
Interestingly enough, what brought me back was Grand Theft Auto Vice City. I couldn't stop listening to the metal station! It was around that time too that someone I work with gave me Opeth's "Blackwater Park". That album made me realize that death metal had so much more to offer than just crappy vocals. So, yeah, it wasn't until I was 30 that I got in to extreme metal...around the time that most people have grown out of it