Very true, but that's just the way things are. Nothing much can influence it. I guess as you get older, though, larger age gaps become more acceptable. I mean, you'll seldom find teens of more than a year or two's difference going out.
My 17 (!) year old cousin is dating a guy who went to kindergarden with me, so my age. I just remembered that. And she has been dating him since she was 15 and he was 20.
Age is irrelevant. It's all about maturity.