I'm a girl, and when I was younger I would have agreed that it is fine, but I've changed my opinion.
I'm 23 now and there is no way I'd go out with anyone under 20. The mentality of a 16-year-old is different to that of someone in their 20's, usually the older partner is taking advantage.
There is nothing illegal about it, I know, but I'd think a guy in his 20's who chased after 16/17-year-olds was a desperate creep.