I am nearly 71. From age 17 to 21 and 31 to 65 I ran (like jogging but faster) regularly. Not marathons but half marathons. Only gave up as my hamstrings were revolting. I now walk approx 10k paces a day - on grass cutting days up to 23k. I also do 5 daily sessions of 15-25 minutes and 2 sessions of 1 hour of yoga for flexibility and strength and to counter the effects of sciatica I had 4-5 years ago . (It works - I no longer suffer from it).
I know lots of fit people who continue exercising well into their 80s.. and lots who stopped in their 50s (if they even started) - the majority of the unfit ones tend to clog up doctors and NHS wards with the various ailments of old age - heart, strokes, overweight etc. And used to know lots of dead ones - mainly men who had heart attacks in their 50-60s.. or cancer etc.
All very well to scoff at those who exercise but the secret to muscle tone - especially heart and lungs is to exercise them to the point at which they are stretched to capacity - and then not to overdo it. It is no accident teh countries with no history of exercise but a tendency to abuse alcohol have the lowest life expectancy in the UK, the worst death rates from heart disease and the worst numbers of obese and medically unfit adults..and cities where in parts life expectancy is lower than Afghanistan..
Of course, I may drop dead tomorrow with a stroke - but until that happens I shall enjoy # gardening, walking, yoga and beekeeping (the latter involves lifting and moving boxes up to 40Kg in weight and being close to nature.) Unsurprisingly elderly beekeepers tend to live long and contented lives.. (I hope

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Edit # and do occasional car maintenance : I can still grovel under a car..
The other secret is to maintain a healthy eating style, avoid burned meat (no well done steaks) and too much rich or fatty foods...and limit spicy foods. The prevalence of prostrate cancer seems to suggest that a rich diet tends to increase its risk.. (My BIL and brother both suffered - we tend to eat more simple food and eat a LOT of fruit and veg)