A younger partner....

I have not been in a relationship for the longest time now, but recently I have a colleague of mine whom I like. He's way too young and we have about a 9 years age gap. I know that it sounds better and probably more acceptable in the world that the male can be way older than that female, and of course not that old though. But how come it sounds like a taboo for a couple which the female is way older like 5 years above, and it is okay the other way around. It's a sad thought that there's a different view to this than when it's the male older than the female. Your thoughts would be helpful!