If you are suggesting that a pilot >60 is operating at less than peak performance at the end of sector 4 on day 5 then there is a safety issue. I quote 60 as the common earlier retirement age. Since then the allowable age was raised to 65: the argument would have it that the safety issue is now more relevant. Now the age limit is removed and we'll see captain >65 stuck to their chairs. The only medical extra, I believe, is a stress ECG test. Has any consideration been given to your argument that an aged pilot is not always at optimum level? I doubt it. What is the effect of this age discrimination philosophy in other transport/medical/relevant industries?