When people retire, they get doubly depressed from age and if they don't have structure and activities to keep them occupied. It's best to never "retire," not because of cognitive "use it or lose it" (which was disproven[1]) but because of the harms of slipping into depression.

For example, my step-father was a copy editor for a large government body who was initially happy/go-lucky on retirement initially but is now extremely self-isolated and depressed.

EDIT: 1. https://www.bmj.com/content/363/bmj.k4925