He could have gone on and on, given his status. Instead, he vacated his position and served as a volunteer to counsel students on future job prospects into his early 70s. His primary reason for making the retirement move was opening the chairmanship to the next generation of professorial talent, almost all of whom he had recruited to Swarthmore over the years.
My father was diagnosed with an Alzheimers variant at age 75 (my age now). That means he and Rita had 8 good years free of grinding daily workday responsibilities, before bit by bit he began to lose his mind. My plan was to retire at 67 the same way dad did. The reasons are pretty obvious, I guess.