Hi as Lyne said I still run ultramarathons, I am only 54 but have been on HT for 5 years now.
i push myself hard and most of the time any pain is usually treatment related ie I am not actually injured so I just ignore it and run through it. That does have a downside as sometimes I am actually injured so I have learnt that a sensible training plan stops those injuries.
The same applies to being tired, I am only tired so I ignore it. The benefits of exercise and a few hours sleep outweigh ( in my opinion) no exercise .
i also have learnt that speed/distance is not important it’s just about going out and feeling alive. I plan something good for tomorrow before I go to bed the night before, that way I avoid dark thoughts and stick to my health plan. I am not perfect and have bad days like everyone but most of the time the thought of some form of exercise is enough.
i also book a race, trek or charity event months in advance so I have something to train for as the triple aim of exercise, fund raising and proving to others anything is possible is good motivation to get me out of bed when it’s wet and cold!
i can only say what works for me but I intend to die living if it’s in my control.
One day maybe I won’t be able to do stuff but I don’t want to ever look back and say I didn’t push myself when I could have, no regrets and all that.
Enjoy your run tomorrow, I will be enjoying mine, Kev