Why does there have to be a "retiring age" at all? Isn't the ability to perform a far better and safer yardstick? After all, there's a similar yardstick at the lower end of the industry as well.
How often have we seen posts on this site asking what the requirements are for XYZ Co to even consider a new hire? Usually it's hours related, with some requirement relating to type (endo or ability to gain one). That doesn't work at the upper end - the hours are usually there already as is the experience on type, i.e. a proven record.
So, as some have already commented, aren't the limiting factors the ability to pass checks and medicals?
I suspect therein lies the devil. There will always be a degree of inconsistency between the testing practitioners in the interpretation of what is and what isn't acceptable. The line between pass and fail is, I suspect, broader than most realise because some parameters are subjective and cannot be quantified.
Arguments over the speed of reflex are not always a good measure of ability. Ask around about the number of incidents where, having suffered an engine failure on a twin, the wrong engine has inadvertently been shut down in haste. Happens in fixed- and rotary-wing.
The bottom line for me is: Can the Commander continue to perform proficiently and safely? If then answers are "yes" and "yes", I'll fly with him/her, regardless of their age.
Le Vieux