I can only comment about myself. I had to stop flying on my CAA (JAR) ATPL in 2006 at age 65. I was allowed to carry on as an SFI in the sim without any medical or any other condition ad infinitum.
However, in order to continue as an SFE, I had to maintain a Class 1 medical so that I could keep my ATPL current.
In other words, if I wanted to take a crew into the sim and teach them, I didn't need a medical but if I wanted to examine the same two people, I had to have a Class1 medical!
I carried on along those lines until I was 68 and came to the conclusion that I didn't need the hassle any more.