You should be able to get a work permit at your age, if you are 14 or 15, and this will allow you to work for a business so that if you put a year or two into a certain place - you'll get a raise or two instead of always making the same amount.
I'd recommend a hardware store, thats where I started out. You learn a lot about word working, plumbing, what hardware to use (screws, nails, bolts, washers, etc) and make money(minimum wage) doing it. Keeps you in shape too, hauling around 8'x4' plywood sheets, or 3/4" thick 8'x4' drywall sheets all day is a pretty good workout. There's also going to be a lot of loading and unloading cement/concrete/sand bags that range from 20lbs to 80lbs. Thats if you go for a small store though, I'm not sure about something like Home Depot.
-SW