His grandfather, Sam Ealy Johnson, Sr, lived to the age of 76. The idea that Johnson men died young was just his excuse for abusing his health. Merely avoiding cigarettes might not have bought him much time, but in the unlikely event that he had "pulled a Clinton" and adopted a comprehensively healthier lifestyle (turkey chili?) he could probably have lived to the same age as his grandfather. That would get him to 1986. It's even possible that he could have lived a few years longer with no change in his lifestyle, if only he had not been alone at the time of his fatal heart attack. It wouldn't be remarkable for a sixty-something to suffer a heart attack, recover, and live another ten years. The problem in Johnson's case is psychological. After he left office, he felt like his work was done and he could smoke himself to death. Maybe the best way to prolong his life would be to change American politics so that busy, industrious post-presidencies become a "thing" at an earlier date.