Sanders will be 75 years old on election day 2016.

[rogerashton]

31. Age specific life expectancy --

Among those who have survived to be 75, the expectation of life is for 11.6 more years, i.e. Bernie's life expectancy is 86+.

http://www.cdc.gov/nchs/data/nvsr/nvsr62/nvsr62_07.pdf

I'm 73. Mine is 85+. The figure given in the OP ignores the fact that, by the time one is 75, people who live to be less than 75 have already been eliminated from the sample.

Of course, the probability death within 4 or 8 years is greater than it would be for a person of, say, 42. I'm taking some precautions in case I'm one of the unlucky ones. A careful choice of a vice presidential candidate would be good. Kshama is young and vigorous.

Dementia is really the greater worry. We have lived through two presidents with probable dementia -- Wilson and Reagan -- and the real danger is that, by the time the person's cognitive function is seriously deteriorated, she or he may be unaware of that, and the evidence may not be clear enough for constitutional procedures to remove the sitting president. Bernie seems to me to be pretty sharp, though.