genetics. they matter a ton . read the bios of really old people (100+ yrs old) and nothing really stands out beyond having a lot of family member who also lived a long time. I think a low-stress lifestyle helps a lot too.
Commenting only on their professional lives. Their investment strategy was generally not a high stress one, they clearly enjoy their work so one could assume their professional lives were generally low stress.
They lived frugal lives, with everything needed covered for probably 10'000 years ahead. Large families, plenty of friends and a lot of wisdom. Yeah, I think Charlie and Warren's life's have way less stress than most people do.
This is a fair point. If you exclude the early part of his life, working as an asset manager is easy work. Most jobs are much more stressful. Basically, you sit around and read annual/quarterly reports and try to find the next company to buy. To be clear, this type of asset management is similar to private equity. They are buying whole companies. This business is much lower volatility than buying/selling stocks for fund management. Also: Fewer transactions. So I would say the 2nd half of his life was low stress (outsider's view, of course).