Old age and medical issues
These are two different things, one the system handles fine and the other it sometimes doesn't.
Normal decline with age is gradual, and provided the player keeps getting games into the system it is tracked fine.
I'll give you two players with more than 10,000 games in the system as examples, Johnny Archer and me (I'm 69).
End of 2021: Johnny Archer 771, Mike Page 613
now: Johnny Archer 751, Mike Page 594
And in 2017 I was 625. I think 594 is about where I play now.
Medical issues issues can involve a gradual decline that is tracked and also precipitous decline that isn't. A stroke can be an example of the latter. A common situation is medical issues affect stamina, such that a player can play close to normal but not with a long grind.
For you in particular, I hope you stay as healthy as you can and continue to enjoy playing pool for a long time. I'm sure it was frustrating to get beat by that sub 600. But rather than concluding that is your new normal, I encourage to look more broadly and positively at your record. For instance, the other sub 600 player you faced in that tournament you beat 7-2. And in the same tournament you beat a 625 7-4.
You've played 7 tournaments in the last two years and your match results about match your rating.
