No not at all. I'd say 3 years difference should be the limit though. Example: a 14 year old dating an 18 year old is weird and not a good thing. Just imagine how different they would be thinking and what kind of things they'd be into. However I know plenty of married couples who are 9 years apart. Marriage is a different story though. Both people would be nature enough to have a good relationship even if the age difference is a lot.