In a past life I spent a lot of time researching the reasons behind compulsory retirement age, in airlines in all corners of the (western) world. With very, very few exceptions mandatory retirement rules were predicated on the reqirements of pension funds.
I could find no medical practiconer who was willing to put his or her name to a document stating that pilot competency decreased with age. If someone can produce such a document, I would be very glad to see it !.
Oh, and by the way, that includes Amos2 from the PNG crash thread.