I think it's okay. And I also think it's okay for a woman to date a man half her age - though many more would probably have issues with this. Why does it matter if there's a big age diff for people to date?
Some people, me included, may feel that the younger person is being taken advantage of, especially for young girls with very low self esteem and daddy issues.
People are taken advantage of all the time, especially in relationships. And the truth of the matter is, the younger you are, the more stupid you are. Think back ten years ago, and remember how dumb you were then. Ten years from now you'll look at yourself now and you'll be just as dumb comparatively. But as long as you're an adult, you're free to make any dumb decision you want.
Although it's true that in relationships in general, someone is being taken advantage of to a certain degree (hopefully it's a pendulum that swings back and forth) but when such an age difference is so apparent at least to the outside observers, most people jump to the conclusion that the older person generally have more to gain when dating someone who is obviously much younger.
Initially, it was a bit bothersome. I always thought 'gold digger'. But whatever floats their boat, I guess.