Sarah stared at her reflection in horror. At 52, the crow’s feet around her eyes had deepened into permanent etchings. The laugh lines that once gave her face character now made her look perpetually tired. Her forehead creases had become so pronounced that even her resting face looked worried....

Everyone thinks they know why Japanese people live so long. “It’s the sushi!” “It’s because they’re naturally thin!” “They must have good genes!” Wrong, wrong, and catastrophically wrong. I spent three years studying Japan’s centenarians, i...