Explanation:

Philip Kotler is 86 years old and will never retire; he doesn’t believe in retirement. “Do I ever relax?” he asks in the epilogue of his latest book, an autobiography titled My Adventures in Marketing. Perhaps Kotler relaxes in his own way, but he prides himself on activity. He answers his own question: “I just enjoy producing more than consuming.”

And produce Kotler does; he still works as a professor of international marketing at the Northwestern University Kellogg School of Management, and he continues to write. He’s written more than 60 books, has more than 60 “episodes” (or chapters) in his autobiography, and for a chunk of time, he may have been the only octogenarian who regularly updated a blog.