Gezellig writes:

Recently a 72 yo went blind in flight (stroke?) and safely landed in the
drink in FL. Several comments were that age should be considered in
keeping your PPL. I can see this makes sense /but/ it would prolly be
illegal.

Pilots undergo a physical exam that verifies that they are in robust health.
As long as they can pass the exam, age is irrelevant.

Too old? If so, at what age do you place the cutoff?

Most people will place the cutoff at their own age plus twenty years or so.

But there is no justification for a cutoff.