Define: "Life Expectancy":
This is the average number of years of life "remaining" for persons of a given age according to a particular mortality table. Average age for healthy American's is 77 years 9 months.
Life expectancy is a statistical measure of the average length of survival of a living thing. It is often categorized by things like gender and geographic location. Popularly, it is most often construed to mean the life expectancy at birth for a given human population, which is the same as the expected age at death. However, technically, life expectancy means the expected time remaining to live, and it can be calculated for any age.
Life expectancy is heavily dependent on the criteria used to select the group. In countries with high infant mortality rates, the life expectancy at birth is highly sensitive to the rate of death in the first few years of life. In these cases, another measure such as life expectancy at age 5 can be used to exclude the effects of infant mortality to reveal the effects of other causes of death.
Further details - Life Expectancy: Free Advice from CDC