My answer is the more dominate one...
I recently got into a relationship with a much younger man that I met through work, yay for being a server. He's 18 and I'm in my 30s but he pursued me and made it very clear he was a top.. I figured since he was such a youngen I could change that if we ever got together... I was wrong.
I made the mistake of letting me drive me home one night when I got hammered and then he hammered me, kinda sorta took advantage of me if you want to look at it that way. Anyway, I've never been as dominated, or dominating for that matter, as he is to me.
I hadn't bottomed in probably ten years and now I'm doing it three or four times a day. So my my answer is this, some guys are tops because they like it sexually, and some people top because that's who they are. I thought I was a top for a long time, and now I'm told different