Japan is currently the country with the highest percentage of people who are old, with more than a quarter of the population being 65+ years old.
Considering that Japan's percentage is much higher than other countries, it does make sense that the country receives attention for having an aging population, even if the current fertility rate isn't the lowest in the world.
Since 1960, there have been 5 different countries with the highest proportion of age 65+. The black line in the graph below displays the percentage for the country with the 2nd highest percentage of each year.
Japan's aging accelerated in the 1990s, passing dozens of countries:
Since 1990, no country's growth in this demographic has been as large as Japan's:
However, many countries have started seeing a similar increase in the percentage in recent years:
In the past 5 years, more than 10 countries have had a larger growth in the elderly population than Japan.
If we look at the number of births per year, we can see that many people were born in Japan between 1925 and 1950, and these people turned 65 between 1990 and 2015.
There are so many factors that affect the 65+ population—mortality rate, current fertility rate, immigration, etc.—so it's not so simple, but it would make sense if it were the case that there was a large number of people turning 65 during 1990 and 2015 compared to previous generations, which resulted in the rapid increase in the elderly population.
Those who were born around 1970 will be turning 65 around 2035, so it will be interesting to see how the numbers will change then.
Some other countries probably had a high number of births a decade or two after Japan, so those countries may start seeing the rapid increase in the elderly population that Japan saw in the 1990s and 2000s.
2021-07-18: Updated with 2020 data
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