When a boy becomes more appealing to a girl simply because he is older than her, specifically if he is an upperclassman (junior or senior in high school). It seems many younger girls are drawn to older guys for this reason, even if he doesn't really have much else going for him. For girls, dating up is somewhat prestigious.
I suppose this could also apply in college, but I have not yet come across that scenario.
"Why does she even like him? He isn't very cute and his personality is just so-so..."