I think it all really depends on the ages of the people in the relationship. I mean if an 80 year old was with a 60 year old it wouldn't be that bad at all, whereas the same age gap for a teenager would just be ****ed up.
When you're my age (17). I reckon a couple of years either way is fine. I have this "friend" who went out with someone who was 4-5 years younger than him. I think that it was a bit too much of an age gap; for someone of our age at least, verging on some sort of paedophilia. He's a closet-homosexual anyway though so I'm not too bothered as I know he really wasn't interested in the person anyway. Because as far as I know. She doesn't have a penis...