Seriously though, if I were single and at that age I'd date an 18 year old if I saw a long term relationship in it. I'm not this kind of guy, but if I was just looking to have some fun I'd stick to girls closer to my age.
When I was 23, I'd say 20, 19 is the youngest I'd ever consider. I'm 26 now and I feel the same way (more like 20-21 being youngest). I guess my only reason is because a girl at 20, would likely have a few years on their own for a while and feel more prepared for something long-term.
Sheesh, didn't we have a thread like this about 6 months ago or was that on the Light side?