Most people don’t realize the habit that most reliably separates people who continue to grow intellectually after age 50 from those who stagnate—and it has nothing to do with books, podcasts, or crossword puzzles.

Last week, I met a retired engineer at a coffee shop who completely changed the way I think about aging. At the age of 72, he taught himself Mandarin Chinese – not because he needed to, but because he had…













