What does this Nicholas M. Butler quote mean Many peoples' tombstones should read died at 30 buried at 65?

"Many peoples' tombstones should read died at 30 buried at 65." This quote is attributed to Nobel Prize winner and educator, Nicholas M. Butler. Basically, it means a person (any person) might quit living life to the fullest at age 30 but the person didn't physically die, and was not buried until the age of 65 (when the person's body did die).