Tan - you are absolutely right. Some people can perform safely for much longer into old age than others. I am also sure that most responsible airline captains recognise their limitations as they get to the point at which they should retire and do so. It is, however, a little worrying that some on this forum see the need to fly as long as possible regardless.
The problem is surely for the airline companies - if the government rules that they have to let these people continue to fly regardless, who is responsible when things fall apart because one of their old employees screwed up. Well, obviously the government, but who foots the bill?
There will have to be exceptions where the safety of the customer is involved.