I love this. I've always been more into seeing a younger stud overpower an older guy and make the older guy bottom. If I were with an older man, that's what I'd do.
For me, the fantasy probably comes from this foreign film I saw on Showcase when I was in middle school. There was this hot high school dude that had a crush on his buddy but his buddy was straight. So when he finds out that his buddies dad was gay, he hit on him. The dad tried to take charge of the sexual encounter but the high school dude ended up overpowering the dad and their relationship took off from there.
Ever since, I've had a fantasy about fucking my buddies dads.