As generally used, the term appears to mean no more than “sexual activity I wouldn’t enjoy.” I rarely use it, since it seems to presume that some sorts of sex are “natural” and others “unnatural,” which is a distinction I mostly don’t want to make: I recognize “artificial” and “conventional” as antonyms of “natural,” but how can anything that actually exists be “against nature”?
Maybe the concept people are trying to get at is something like “dysfunctional,” but not having the appropriate biomedical training I’m going to leave that one alone. Nothing “unnatural” or “perverse” happens when an adult male is attracted to adolescent girls; the wrongness of acting on those desires isn’t a biological wrongness.
That said, I think I’m willing to assert that wanting to have sex with someone who doesn’t want to have sex with you is perverted. By “wanting” I don’t mean fantasizing about it, or imagining that the object of your fantasy has a a change of heart, but wanting to actually have sex with an unwilling partner: someone who consents, if at all, for some extrinsic reason. As a friend of mine once said about dentists who take advantage of patients under anaesthesia: “That’s not sex; it’s just friction.”
Can’t Dennis Prager just buy himself a blow-up doll, or find a consenting nanny goat?