I have been thinking about how careers in the 2nd half of life are different. In fact, I claim that the idea of a career in the 2nd half of life is a relatively new concept.
My father was forced into retirement at the age of 59 in 1978. He did not want to retire, so he decided to teach college economics (he had been an economist for the NYSE for 25 years). He did not have his Ph.D. and had a really hard time making the transition because everyone expected him to retire.
Things have changed. We are living much longer. I plan on living both a longer and healthier 2nd half of life than my parents.