Not sure if that's a store policy or child labor laws at work. Child Labor laws can get pretty intense.
Where I live, the local McDonald's figured it'd be totally OK to hire an 11 year old... then of course the manager got in trouble for doing so. That was truly an annoying McDonald's visit. He was just standing there behind the register wandering around in the back going "What's that? What's that? How do you do that?" in the most high pitched hyperactive tone possible while I'm just standing here looking at him going "this kid can't even be 12."
No, small towns, you can NOT overthrow U.S. law by making up your own rules, especially if you work for a million dollar chain restaurant. Can't even count the times we've been over this.