When I was seventeen I drew the line at two years, I wouldn't want the gap to be much bigger than that. 17 and 14 could mean two years and one month difference, or it could mean three years and eleven months difference...I think...I tend to screw those calculations up. My point is though, there is some leeway there. And yeah the other guy was right, as people get older the gap doesn't matter as much because it's a ratio sort of thing. It wouldn't be weird at all for a 20 year old woman to go out with a 23 year old man.
I'd like to say "as long as the two people are comfortable with it it's okay, and it shouldn't matter what other people think" but in reality, it does matter.