When Is the Right Time for Executives to Retire?

When Mark Cohen retired from his role as director of retail studies at Columbia Business School last month at the age of 75, he was confident he was far better at the job than when he started his career as a professor in 2006.

The reason: a few years ago, the former Sears Canada CEO, sensing a rapidly widening “chronological gap” between himself and his students, enlisted the help of a young teaching assistant. She helped him turn his…