I'm the same way. I've never been with someone sexually, aside from my bestie kissing me to show me how lol, but whenever I fantasize or just think about sex, I'm never using mine. People are quite shocked that I have NO desire whatsoever to get a ->-bleeped-<- haha. And now knowing I'm trans, and thinking about myself as a woman, I think of someone going down on me having a vagina, rather than a penis, and the idea is amazing to me.