I like your optimism, and every octogenarian who can stay sharp is an inspiration to us all.

But if you look at aggregate data on chess players' ratings as they get older, or university professors' publication rates (and citations on the papers they do publish), it's really hard even for strong-willed thinkers to stay on top of their craft in their 60s and beyond.

For every Warren Buffett in business, there are a lot of Sumner Redstones ... holding on to power, but quite erratic as age takes its toll. Getting old is nasty stuff.