Are you implying people don't change after 18? I hope that's a joke. People change physically and mentally throughout their entire lives. There's no magic number for when you're suddenly mature and ready for sex or relationships. Most 30 year olds, or even 25 year olds, would think the typical 18 year old is an idiot. Conversely, I know adults who are less mature than their kids. The only reason most of us are frowning on this is because it's burned into our heads that if anybody above 18 is with anybody below 18, it's creepy, but anything else is good to go. Legality is the only thing stopping a lot of men from 20 to 30 from dating teenagers. Girls like older men with a more rugged look, and a lot of guys like younger girls with a fresh, unused, slender rather than curvy look. If laws weren't a factor, the only thing people would deem creepy would be being interested in prepubescents. That's downright disturbing. I voted I don't know what to say, because 12 is right on the edge of that prepubescent line. Some look as good as any 16 year old, and could be mistaken for one if they fake themselves out in makeup and whatnot, but others look about 7.
Most males are actually "hebephiles". Males are programmed to be attracted (well, physically attracted either way) to females in mid puberty (the difference today is that people reach puberty earlier). The reason most don't act on it or even admit it is laws.
Fixed. I guarantee, if it was legal, there would be a lot more men dating young teenagers