I took to booze fairly early in my life. I saw others use it in my family, and it was always readily available. Even after experimenting with other drugs in high school, I always came back to alcohol. The illegality of other drugs scared me off, and I think I just enjoyed the sensation that alcohol gave me.
I'm aware that I could probably replace booze with another drug or behaviour, but alcohol will always be my "true love" (I mean that in the most dysfunctional, destructive way possible).