Depends, are you getting a plan or a prepaid iphone? I was allowed to sign for a prepaid at the age of 16 with only a driver's license, or some other form of identification needed, for me it was a learner's license. Im guessing that the iphone isn't considered any different to any other prepaid iphone. Thing you'd have to look for is wether they will stock the iPhone on friday with most places lacking them.
Yeah but why would you WANT to buy prepaid for $700+ personally i wouldn't bother.