Personally I think it's ok to find younger people attractive. I recently saw the new Harry Potter and made the off hand comment that the girl who played Hermione was turning growing to be quite attractive.
In my honest opinion, however, if you are well over 18 and your are getting your rocks off on young adolescent, or worse, pre-teen children, there are psychiatrists that can help you.
Sure, in colonial days and earlier, it was common place for a older man to have a much younger woman, and sometimes vice versa, but still doesn't really make it right.
Besides, I like my girls when their plumbing has fully developed.