Flying is not unique in needing to address the issues of an aging group of participants. We often hear of the problems of an aging population on healthcare systems, but less about the aging doctors. There is an increasing amount of research egged on by the fact that we havent enough doctors in the 1st world, and we cant afford to let them go due to age!
The evidence is that decision processing changes. Younger doctors make decisions based on many inputs with an output determined by a protocol. Older doctors use experience and need less inputs but often have a better output. Although the older doctors find it difficult to cope with night work, fatigue itself is of little importance.
As a result we believe there is scant evidence to stop older doctors working even at the cutting edge. Pilots have the added hurdle or check of needing a medical, and here again the evidence is that a 70 year old today is less likely to experience a sudden incapacitation than a 60 year old just 20 years ago. Flying is far more sedentary than many medical specialties.
So whilst I would never criticize anyone deciding to retire, I do have concerns at anecdotal comments about older people being somehow less safe.