You can be hired at 16/17, its just you are limited to 20 hours maximum when you are in school or in general, and you can't be a keyholder (where you have access to open and close the store) plus your access in the Gamestop computer is limited (i.e. you can't send out stuff, view shipment, check e-mails etc). That is what the rule was over here in Southern California when I was working there.
But honestly RiceBo1 Gamestop is a shitty place to work for. You will be hired in as a game advisor, and that is the lowest of the totem pole. Your pay will be minimum wage most likely, and you will be given all the bitch work to do. Plus thats not to mention the constant nagging for pre-orders/magazines subs you have to sell to keep your job and hours etc.
Although it varies store by store, district by district Gamestop could be okay to work for if you have a cool staff, manager and DM etc. It was cool for me when it was EBgames, but once Gamestop took over they started clearing out all the EBgames managers and managment etc or at least drive them to quit and replaced them with people who didn't know what the hell they were doing. Eventually the store I used to have fun working at became a true Gamestop, and everything went downhill from there. Leading to me and five other employees all quitting on the same day this past April because we all had enough of the bullshit the manager, district manager, and the company in general were giving us in our area.
So bottom line Gamestop just treats their employees like shit, and doesn't care because they know a lot of people would love to work at a game store, and all the people on their payroll are just expendable, and easily replaced. Try applying at a BestBuy or Gamecrazy if you have those in your area, but if you are still interested in Gamestop be warned.