How do you know all of them feel the same way? Not all young people think the sameWhen people who are young in the first world say they are attracted to older men they often don't mean significantly older. A middle aged man unless he looks young or handsome is not the picture of loveliness. Money is attractive to some I suppose. How about you devise a poll asking if people are open to large age gaps and see how receptive they are? Or better yet look at average age gaps of married couples. It likely isn't 15-20 years on average.
Some may like older men. You are just generalizing.