I have played with 8 year olds here in Japan, and I have played with 14 year olds back in Canada.
I've had young players here offer me full magazines when they heard my gun starting to shoot dry.
I've had kids in Canada lie to me and try to get around the age verification system. One from Nippawin, SK even offered to give me $50 to look the other way to verify him. I've had kids back home lie, cheat and steal from my team-mates (Layne Meier of Regina, Saskatchewan for example, his username was 'Sasksoft' and ripped off a FUCK ton of money, but didn't get charged cuz he was 16/17).
So you ask why kids are looked down upon? Because we remember the shit-heads, not the good ones.