Philosophically, working until you're n years old is optimal -- for some value of n that I wouldn't think to dictate to anyone else. Maybe it's 50, and maybe it

Philosophically, working until you're n years old is optimal -- for some value of n that I wouldn't think to dictate to anyone else. Maybe it's 50, and maybe it's 500. I don't know how it'll work out a few centuries from now and neither does anyone else. With luck maybe some of us will live long enough that we'll be able to offer more than glib speculation. Until then, to the extent that I can, I prefer to err on the side of not killing billions of people.