I can't answer for the parent comment, but after working just when I wanted to for 20 years (onsite at Google and Capital One were the only exceptions in a 20 year period), I finally decided to really retire March 2019 (except I still write).

My diet is even better now because I have time to cook real meals following a hybrid of Dr. Fuhrman/macrobiotic diets. I bought weights, and hike/walk an average of 90 minutes a day, and except for worrying occasionally about how family and friends are doing with covid-19, life is peaceful and fun.

One thing that I think is vital is having goals. For me that is spiritual development and studying specific tech, programming languages, etc. I have been an artificial intelligence practitioner since the 1980s but I have very little experience with probabilistic programming, graph models, etc. My goal for the next year is kicking my knowledge up a few levels. These are the only goals I have, and that is enough for me.

Great question, this is why many men die shortly after retirement (in the first year even!)