Looking at some veteran sites on FB, you're getting all the usual bravado of "Yeah, I'm going, who's coming with me?" and "Lets go sort the ruskkis out!", then you look at their profiles and they are middle aged to old, overweight, couldn't run for a bus.
They might have been the mutts nuts 20 or 30 years ago when they were younger, fitter, trained, current and able, but now they would just be a massive liability.
After 27 years service, I'm old, broken and out of date. I've had my war, I'm staying at home. If by some miracle the war gets to the UK, then I will fight.