Funny, I was talking with another student about this sort of thing today. I'm 45; this guy was 52. I hope to test for shodan in about a year if I'm lucky. I certainly try to stay in good physical shape, and getting up 100 times after being thrown across the mat certainly helps. I think I will be in good physical shape. But, will I be in the same physical shape as a 22 year-old taking the same test; probably not!
Then on the other hand, I tend not to place myself in situations that 22 year-old men may place themselves in, so I am a little less concerned at this stage in my life about real, bar-room brawl stuff than I might have in the past. All I want is to have a physcially and mentally demanding test and demonstrate a good grasp and facility with aikido principles. That's really all anyone can ask for. I think anyone HAS to be in good physical shape to undertake a shodan test, but it may not be the same level of physical shape for every one at every age. Like the old army commercials said "be all you can be". That's all anyone can ask.