Life expectancy does not go down by 1 year for each year that you age. One way to see this is to look at the fact that, in the US, male life expectancy is 34 years when one is 45 (total of 79 years); yet, the average 80-year-old male is clearly going to live to be more than 79 years old, as they have already survived all of the things that were going to kill them by the age of 79.
Useful data: https://www.cdc.gov/nchs/data/nvsr/nvsr65/nvsr65_08.pdf