Hey all, Does this way makes sense to determine the number of people in each catagory?

For example, If the life expectancy in a country is 80 years and the population of the country is 50 million then,

80 / 50 = 0,625 people in each year catagory.

Lets say that I want to know the population segment from 0 to 16 years old. Then

0,625 x 17 = Around 10,6 M people.

Does this makes sense?

What other possible way can we use to determine lets say the population segment from 0 to 16?

Thanks

(edited)