This is the rationale behind age-based standards. You can easily, and accurately, argue that the job requirements don't change with age, but since our abilities do, having standards that recognize that fact continues to hold younger personnel to a more realistic standard of excellence...or minimum competence.
As someone in another thread pointed out, lots of things have changed in the Army since I retired, but at that time both the "passing" and "maxing" standards on the APFT changed with age. My understanding is that the passing scores on the Marines PT test went down, but the max scores did not. (Or maybe it was the other way around? It's been a long time...)
According to this article it looks like the Army is finally implementing changes to the PT test they first started talking about ten years or more ago, including having the "Combat Fitness Test" as well as a "PT Test."
FWIW -- which is nothing -- my opinion is that having two tests is stupid. I'll head down to the Legion Hall now to perch on a bar stool and bitch about how easy these young punks have it thee days...