Yeah, inevitable age hits some faster and harder than others.
I know some guys who are struggling to maintain a semblance of physical fitness in their 40's and 50's, but others (retired) who are still fit enough for many LE activities in their 60's & 70's.
I know one retired gentleman (former detective, firearms trainer & armorer) who isn't spry enough for foot chases or one-on-one anymore, but who is more than fit enough for firearms activities, and he's in his early 80's.
Being in my early 60's, I'm already serving in a reserve capacity for some activities that benefit my agency. I've certainly known some reserves older than me, too. Maybe the British police could learn something from how America still relies upon its retired cops in a reserve capacity in some instances, although I've no doubt the practice (and policies) vary quite a bit geographically.
Shooting is a perishable skill, though. Considering the British apparently don't like their citizens (including retired cops) to actively engage in firearms training & practice activities, I could see there being some necessary training needed to try and rekindle those skills.
It would be a much easier task in this country, I'd imagine, as a lot of American cops still enjoy engaging in firearm shooting hobbies (and even competition) after their retirement. Also, having to come back periodically to demonstrate proficiency for renewing retirement ID cards (for continued CCW authorization), as well as annual qualification for LEOSA, can help keep current some adequate level of skills.