Life expectancy as just a single number is a pretty useless static. It says almost nothing about any single individual.
First off usually when not specified a single LE number is a life expectancy at birth. So that 79.25 years is likely for a baby born this year in the US.
Second and more importantly as you age your life expectancy goes up. Basically you have out lived every one who has died and dragged the average down. At 77 you are expected to have 9 more years of life. It is not until you are 111 that you are more likely to die this year than not.