Is is, and always has been, the easiest thing in the world to devise a combined service fitness regime.
1. A common basic entry level fitness standard that everyone must past, regardless of age or sex (obviously with a very low bar)
2. A role specific fitness test which everyone must pass for their specific role (obviously with a very variable bar).
3. A thorough annual medical for all.
Why does this not happen? Partly because of the cost of providing said annual medical and partly because of empire building by the fit brigade and their devotees. You've only got to read between the lines of some of the "we're-jockstrappers-ain't-we-great" posters above, to see where I'm coming from.
PS BTW, TOFO is actually old & fat but I can still shin up a Munro in less than 2 hours (from sea level).