Is it illegal in the US to work someone more than 70 hours?

My bf is currently working retail for an 11.00 hourly wage and is considered part time. He doesn't receive any benefits. He told me today that this past week including today he'd have worked more than 71 hours. He has been scheduled for 9 hour shifts almost everyday. Next week, he will be scheduled for much shorter shifts. Either way, I know his hours will come out to more than 80. Will he get paid overtime if he isn't a full time employee. Shouldn't they make him a full time employee if they are going to work him this many hours? Isn't it illegal to work someone this much in one week?