You can share your wisdom and be of great value to the public without being in public office.
At some point, though, you've gone from useful adult into honored elder, and while I'm not suggesting we put them all on ice floes, they shouldn't be running the country, especially since more than a few of them clearly don't even know which country they're in, let alone how to run it.
If you can't walk, are having strokes, have developed dementia, and generally just sit around staring at the wall like my cat, perhaps it's time to gracefully retire and go spend the rest of your life doing conferences and speaking engagements and whatever the hell else you want, not trying to legislate.