I've recently decided it was time to call it a day at age 75, no known health issues but I could feel myself taking longer to compute my workload of information being thrown at me, therefore I felt I was getting behind the aircraft.
I will add, this was in the UK, prior to that most of my flying was when I was living in Florida before returning to the UK. If I was still in Florida I think I would still be flying for quite a few more years.