Health is affected more by social and economic factors than by microbes or arterial plaque. Expresidents swim in bennies:
1) On a social level they're as successful and fulfilled as it gets, they are given a deference and authority for the rest of their lives, and that is an alpha position that lengthens lifespan;
2) they receive the world's best medical services, services paid for with other people's money, so when one has a hangnail it's taken care of at no difficulty to himself;
3) counting all the benefits they get from pension to staffing to travel expenses, they have effective incomes that put them not in the politically infamous 1% but more in the 0.1%, so they don't have the economic pressures and restriction that erode the health of most of the elderly.