The additional criteria gets rid of the wanna be gang bangers, and trust me in the Vancouver area there are lots. One those morons waving an airsoft pistol or AEG around in thier car or on the street will not help the sport.
Besides which age verification is about judging maturity, not giving anyone who wants it access to the buy and sell. It takes more than 30 secs to make that judgment.
So if they come and see me twice, I can make an informed decision. They do not have to play just get themselves out to the field.