The Country Similarity Index attempts to quantify how similar countries are to each other relative to other countries. The index is a statistically-based way to measure this. 20% of the index is based on demographics. 10% of a country’s demographic score (2% of the overall Country Similarity Index score) is allocated for age. The statistics included the median age of a country’s people, as well as the percentage of elderly people and the percentage of children. The following is an explanation on how they were calculated:
Median Age
There is a large difference in the median age of the population in different countries. Japan has the highest median age of any major country at nearly 50 years old. In contrast, the median age of a person in Niger is just 15 years old. Most of the youngest populations are located in Sub-Saharan Africa. On the other end of the spectrum, European countries tend to have some of the oldest populations in the world.
The CIA World Factbook is the main source of the data:
https://www.cia.gov/the-world-factbook/field/median-age/country-comparison/
Countries were grouped by the following median ages of people:
11.5-15, 15-18.5, 18.5-22, 22-25.5, 25.5-29, 29-32.5, 32.5-36, 36-39.5, 39.5-43, 43-46.5, 46.5-50
Elderly
Unsurprisingly, the countries with the highest percentage of people over the age of 65 also tend to be the countries with the highest median age. Japan has by far the highest percentage of people over 65 at around 30 percent. The next closest, Italy, is under 25 percent. Although Sub-Saharan African countries have few elderly people, Qatar actually has the lowest percent of people over 65. One big reason for this is that a high percentage of its population is migrant workers. United Arab Emirates also has an extremely low percentage for the same reason.
The United Nations is the main source of the data:
https://www.theglobaleconomy.com/rankings/elderly_population/
Countries were categorized by the percentage of people over the age of 65:
0-5, 5-10, 10-15, 15-20, 20-25, 25-30
Children
South Korea has the lowest percentage of people under the age of 15 at around 11 percent, but Japan and Singapore also has an extremely low percentage. In contrast, the Sahel region of Africa tends to have the highest percentage of children. In fact, nearly 50 percent of people in Niger are under the age of 15. These also happen to be some of the least wealthy nations in the world and their infrastructure is not well developed.
The United Nations is the main source of the data:
https://www.theglobaleconomy.com/rankings/percent_children/
Countries were categorized by the percentage of people under the age of 15:
9-16, 16-23, 23-30, 30-37, 37-44, 44-51