If you don't work, what are you going to do sitting at home alone -- doing nothing? The way I see it, if you start work at 20, you get exp at 30, 40, 50, 60 and then you can train and mentor people at 70, 80 or 90 -- training is important, very very valuable work.
If you have a team of tree choppers who have 8 hours to chop down trees, a wise old man or woman will spend the first 4 hours to sharpen their minds with their experiences so that the team can chop down trees or overcome challenges faster with sharper axes or better problem solving/ critical thinking skills (Abraham Lincoln).
Even if they have grown frail, weak and old, that's by nature or divine design. I bet I can learn so much more from following the Temasek CEO (you) on Facebook than anybody else on LinkedIn or reading anything else available.