When I retired in my early 60s, I “jogged” 10 miles every day for almost two years at a 7:00 pace.
I had zero fatigue, and almost zero injuries.
Maybe once or twice a month I would close my last mile with a 6:20 pace. I still had zero fatigue at that pace, but usually with minor injuries, and once with a severe hamstring pull, which ended my almost two year streak.
Now that I'm almost 70, I have had to cut my mileage back to six miles a day and cut my pace back to 7:30 to limit injuries.
Currently, I usually have about one month of injury down time per year, plus chronic Achilles tendinitis, which I've had for 50 years!
^-—— I’ll have what he’s having.