I have a weird fantasy (fantasies)

Hi there,I've been straight my entire life but I've always had a fantasy of anal sex with much older men. I'm 22 and when I mean older I mean 50s plus. There's no sexual attraction and I don't find them attractive in any way. I just like the idea of an old man having sex with me. I don't want any cuddling or kissing and all of that either. When I was younger I used to cam to old men and show my bum too. I'm in a relationship with a girl now and I'm very happy with her and don't want to change things. What would you say I ? Many places I've google say I'm gay, but I have no interest in guys my age, don't find men attractive and really the fantasy is anal only