For awhile I thought I should limit myself to 10 years younger. That seemed to be a good limit. At that age difference you can still discuss just about anything. The older person can impart wisdom, the younger person can teach you about things you didn't know existed in this world.
But now I think ten years younger than me is too old. I'm going for the 20 to 24 age range.
These young men are not jaded. They are full of hope and excitement for life and they still respect the idea of purity - they don't expect you to sleep with them on the third or fourth date.
So if you were thinking of fixing me up with someone, check his birth certificate. It should say something like 1985.