All certification requirements are set by the FAA. The number of hours of training, classroom time vs. hands-on training, written testing, practical testing with equipment/evacs, physical requirements, annual recurrent training, etc, etc. The guidelines and specifics are all up to the FAA, and they do send people around to airlines' training centers for monitoring.

The original poster asked about physical strength and whatnot, and there are some very basic assessments made during a FA's initial training cycle. After that, there is no physical exam of any kind. FA's can work forever so long as they can open the doors in the training department during annual recurrent training. Me personally...I think we should have some kind of physical exam once every few years. Nothing as stringent as the pilots go through, but there should be something imo.