I think attraction to younger women is largely instinct: more capacity to bear more children. Having said that, I want to stress that older women are still attractive. I'd take an older in-shape woman any day over a young fatty.
As long as my wife stays in reasonable shape I can't see myself straying for a younger woman.
Women don't seem particularly attracted to youth - quite the opposite. I think that would have to be one of the great plusses of being a male.
Is it burnin'? Well, f-ck, now you're learnin'.