A lot of these guys were teenagers but it requires a lot of time and effort to reach there in the top 20s. So, they became adult by then. And teens tend to change their interests so quickly. They joined this site, got bored, jumped to another!
To be a top member with that amount of Xper takes time and a lot of it. As in years and years... that's why it's impossible to be in your teen years and accomplish a Xper level like that. You'd have to be on here A LOT.
Well teenagers are at school all day. I'm sure those top members are either college students, housewives/househusbands, office workers, or people who work from home, all of which probably have more time to spend on the internet than teenagers.
Most teenagers don't give solid advice? Or just come and go really quickly?