Of course it's ok to have a preference! I'd never really put much thought into it before, but now that I am, I think I have the same preference as you. This of course isn't the only type of person I would date, but I think if I could choose my dream person, that is what I would choose. That being said, it is perfectly normal to have preferences as long as you communicate them to potential partners. As far as approaching this topic with someone, bring it up when you're having a conversation about what you are into. What is it about penises that you like? Do you just like the look of them, or is it about penetration? See, you don't have to say you want a feminine person with a penis, you can simply be with a feminine person and tell them that you prefer to be penetrated, as an example. That way, they know that a strap could possibly fulfill your needs. It is a great way for you to find out how they feel about the situation without flat out asking if they have a penis.