I have to say I rarely if ever get to do organised / compulsory PT; either it doesn't exist (my current unit) or the bosses suddenly find things for the officers to do just before PT starts! As a result, I have always done my own PT, usually 45-60 mins after work, interval training / light weights but still manage to get light blue on the tests. Now as the only Olympic medal I am ever likely to be in contention for is the most useless individual in the stadium, I would contend that means that getting and staying fit is reasonably easy if you keep it up.
The way I see it having observed my parents, when a gentleman reaches a certain age, the idea of fitness subtley shifts from being able to pass a military fitness test to staying healthy, keeping the old ticker going long enough to enjoy your pension and generally being in a fit state to enjoy life. So if I were you, I would be looking to do enough fitness to keep me mobile and enjoying life whilst also balancing out the odd drinkie and slice of Brie after dinner.
I would have thought a 40 min walk up and down hill would do wonders, but you might also want to throw in the odd light weight session once or twice a week to maintain strenght, tone and make use of the fact that muscle burns quite a lot of calories lb for lb, so more muscle means you can enjoy that extra drinkie
