Life expectancy equals the average number of years a person (men or women) born in a given country is expected to live if mortality rates at each age were to remain steady in the future.

In Japan in 2015, the average life expectancy at birth for man and women was 83.7 years according to the World Health Organization (WHO). The women on average were expected to live at least six years longer than men in Japan.

Also, the life expectancy figures for Japan reflected the quality of healthcare in the country as well as other factors including ongoing everyday stress, obesity, HIV infections, etc.

More Info: en.wikipedia.org