Social structure might turn out to be more important. In Sardinia, a cultural attitude that celebrated the elderly kept them engaged in the community and in extended-family homes until they were in their 100s. Studies have linked early retirement among some workers in industrialized economies to reduced life expectancy. In Okinawa, there’s none of this artificial punctuation of life. Instead, the notion of ikigai — “the reason for which you wake up in the morning” — suffuses people’s entire adult lives. It gets centenarians out of bed and out of the easy chair to teach karate, or to guide the village spiritually, or to pass down traditions to children. The Nicoyans in Costa Rica use the term plan de vida to describe a lifelong sense of purpose. As Dr. Robert Butler, the first director of the National Institute on Aging, once told me, being able to define your life meaning adds to your life expectancy.