I’ve been an Aviation Medical Examiner for 40 years (and a pilot for 53), and it is clear to me that individuals vary widely. Some pilots are losing the edge at 55, others are energetic, sharp and still on top of their game at 75. The original age 60 rule was entirely arbitrary, pulled out of thin air by a committee of non-aviators at the AMA. There have not been safety-related problems since Congress raised the age to 65. There is no reason why pilots who are sharp, who continue to pass every-six-month medical exams and perform well on recurrent training and checkrides to fly to 68 or even 70.
Obviously it won’t be for everyone, and contracts should be structured so that those like William B who are just too tired for the airline life at 65 or earlier can retire without penalty. The number of forcibly-retired airline pilots who jump to flying equally sophisticated jets under Parts 91 and 135 are testament to the foolishness of a one-size-fits-all mandate to throw them out of airline cockpits at 65.