Why do people say women mature faster than men?

I was asking one if my female friends why she always dates guys older than her and she said its because women mature faster than men and guys her age are immature (I'm her age). I asked her what she considers immature and she said we only care about sex and are perverted ECT. Then I asked her isn't it immature to not give a guy a chance because of his age? I think they go after older guys because if they can get an 18 year old to like them they feel accomplished, like they got a trophy.