Perhaps controversial, but after 65-70 continuing working is fine but the type and focus of work should change because if not, the work will be at the expense and harm of the next generation.

After a certain point the focus should no longer be on doing work first hand, but should be working to help, mentor and advise others to provide them a path instead of occupying the top.

Fostering the next generations should be the goal, not occupying career space until the grave.