I have a great friend who is exactly 5 years younger than me.
We joke about our various aches and pains working to a schedule - and his schedule is 5 yrs behind mine.
When i was a kid, post exercise muscle 'stiffness' turned up after around 20 hours, and stayed for about a day.
Now i get pain the same day, worse over days 2-3 and then it starts to ease.
Tendons take 2-3 months now.
It is all rather tiresome.
I see young people zipping about with disturbing enthusiasm, injuring themselves with a belief in their own indestructability (runner's knees, tennis elbows, pushing through the pain, ignoring back twinges, training before adequate recovery...) and i flinch. Been there, done that. And now all those injuries have come back to haunt me. Permanently. I can trace my calf twinges to that terrible pulled muscle I had in my 20s, and my shoulder to the competitive swimming in my teens, and my back to the lifting I did during my first ever Saturday job.
Sorry if that is depressing, but don't worry - if someone had warned me all those years ago, i would have ignored them too.
we all think we are immortal when we are young.