In my early 20s, I dated someone 9 yrs older than me, we were both in school kinda the same points in life. It was my only ending of a relationship. Looking back I was mature enough to see that I was not looking to settle down and she was, I didn't want to waste more of her time.
I think as people get older the age discrepancy is less an issue, however the 18-24is range there should be plenty of fish in the sea and 5 years can make a huge difference. As we age there is also less potential mates to choose from.
Still in high school? Maybe 1-3 year different at most.