I have never topped a man and I probably never will. My current partner of 9 years is very much a top like yourself. I never had an interest anyway.
I guess you can call being sexually submissive a fantasy. I think of it more as a lifestyle choice. The rest of my life is about being responsible and in control so not being in control sexually balances me out.
My advice would be to introduce anal play into your masturbating sessions and explore what it would be like for yourself.
Often beginners don't like anal because they are relying on the top to know what they like and how they like it.
Learning how to work your prostate will add a new dimension to your sexual activities regardless of being a top or a bottom.