I've been on both sides of this "ball".
When I was 15-18 yrs. old, I never wanted to date anyone younger than me. I didn't even want to date anyone remotely near my age. I wanted older, because as a 15-18 yr old, I wanted something that was going to last.. and most people between those ages, don't.
Once I reached 18, and had a considerable relationship with a 23 yr old Mother of 2, that ended anything but well.. I decided that it was time for a difference of opinion. That's when I really met Desiree, who by all rights is the closest to my age as anyone has come.. that I've been interested in.
Once I got older, around 20, I questioned dating younger, but also questioned the dangers in it. My 1st fiance' was a 16 yr. old, when I was 20.
That worked okay, but had a terrible ending and mainly because she was too young to get into a serious relationship. Which leads me to my firm belief, NOW, and that's NOONE under the age of 18, is going to look for a serious-enough relationship. I don't give a shit what you say, it's not there.
So on conclusion, my thoughts on the subject are like this..
10 yrs. + or - are not horrible. I was 19, in lust with a 30 yr. old. Anything beyond that though, is pretty much overkill. You risk not having anything in common, and a decade of differences.
It's better to stick to those near your age grouping, but 5 yrs is just like 5 months.