I apparently look a bit younger (or so I'm constantly told), and the two serious relationships I've had have been with guys 2-3 years younger. I mean, it's not a big difference, but hey - if a guy approached me now in his late 20s it wouldn't be a deal breaker! (I'm mid 30s).
P.S. I don't go for them, they go for me! I've never actively gone after a younger guy, but if I meet someone, get along with them, a few years isn't a big deal