Actually, it doesn't stand to reason that men's sexual preferences would drastically change with their age, men don't suddenly become attracted to grannies as they become older, pretty sure most men would get with a younger women if they could. Typically, rich and powerful men have younger wives than normal.
As I've already noted, I haven't been talking about whether it's alright for older men to be in relationships with 15 year olds, just that attraction is normal. So perhaps we can get past these nonsense inferrals that anyone who finds anyone below 20 attractive has something wrong with them. Also, I don't think you understand what incest means.