It's hard to put conditioning requirements on a level anywhere close to officiating professional athletes on people that are approaching or have already exceeded the age of 60 years old.
I have noticed that they have indeed trotted some younger guys out there over the last few years, but how conditioned can they expect the majority of the officials in the NFL to be when they are approaching, if not exceeded, retirement age?
It was really bad in the 90's if I recall. It seemed like they stopped by the retirement home to pick up the officials before each game back then.