Why Retire At The End Of Life?

Robin Hanson wonders:

Humans and other animals were designed to learn important skills during childhood playtime, which helps explain our start of life play. (Most animals only play when young.) Our habit of deferring so much play into the end of life, however, is a bit more puzzling. Our ancestors didn’t do this – it is a feature of our modern world. While encouraged by laws and regulations, the idea also just seems to appeal to many. But why, for example, doesn’t the idea of spreading a decade of play from age 65-75 across the four decades from age 25 to 65 appeal more? Why not want a year off out of every four, or a week off every month?