Well, in my opinion, there are many people who would say that isn't right or gross, because of one being a younger age. But if you would take the same age gap with different ages, like I did, it wouldn't be a problem because they are both adults. So I think its the young age of a person that scares them away from the idea of being with someone that old.
It isn't wrong and it could be great but if things get serious they really need to think whether a longterm relationship could work. A 20year-plus age gap is much bigger when one is turning 80 and the other still in their fifties!