Look at the "Rich but Shrinking" graph in the article. I'll report the numbers here for simplicity:
Country / number of babies per woman
Israel: 2.9
Mexico: 2.1
France: 1.8
US: 1.6
Australia: 1.6
UK: 1.6
Germany: 1.5
Canada: 1.5
Spain: 1.4
Japan: 1.3
Korea: 0.8
(all numbers as of 2020 except Korea)
Now, there are a few things happening with this.
1) Numbers are wrong. Based on World Data [0], Spain is 1.2, not 1.4.
2) Notable countries are missing from the list: Hong Kong (0.9), Singapore (0.9), Italy (1.2).
3) "Korea is the world’s fastest-aging nation among economies with per capita GDP of at least $30,000," conflicts with the fact that you include Mexico in your list of countries (Mexico's GDP is below $30,000), just to make Korea's problem look worse.
[0]: https://data.worldbank.org/indicator/SP.DYN.TFRT.IN?most_rec...