We'll I'm friends with few college guys. They tend to like younger high school girls bc they are innocent & not extremely sexual yet. Once girls get to a certain age they can get really, really sexual. & some guys believe it or not are not attracted to that.
Maybe they actually like the girl that's a bit younger. It's possible you know. Maybe they think it's easier to take advantage of a girl that's a little younger. But not every person that's with someone younger is some super-perve or something But personally I don't think it's a big deal if someone's a few years older, age difference has never bothered me.