I don't know it a person has much choice if they fall in love. Reason goes out the window. Even if there is an extreme difference in ages, there is hope for happiness.
Several studies were done on May-December romances, and found that difference in ages had less effect on marriage than other things. It doesn't make sense to me, but research is research; and age difference does not have much to do with marriages.
Personally, I don't think I would want to have a relation ship with a young girl or an old lady. Five or ten years difference would usually be okay. If one of us is 30, and the other 20, it would probably be okay with me. But, I would shun any relation ship with a 16 year old girl if I were 26.
But, like I said in the beginning, one doesn't have much choice if they fall in love.