I believe the number is closer to 20 million.
I stand corrected, it's about 8 million for the 18-30 population. There are about 11 million in the 30-40 group. So yes, 19-20 million in the group I initially cited.
https://www.cia.gov/the-world-factb...sternEuropeAndNorthAsiaPopulationPyramids.jpg
I have heard stories that the Russians quit collecting accurate numbers on the population about 15 years ago. Which means that the numbers of the 15 and under population is just made up. Anecdotally women are having a lot fewer children during that time, so the numbers may be much worse than reported.
Many European countries have the same sort of narrowing of the population among the younger generations
Population Pyramids by Region - The World Factbook
A number of East Asian countries are seeing similar narrowing
https://www.cia.gov/the-world-factb...4f9dedd21/EasternAsiaPopulationPyramids-1.jpg
Thanks to immigration the US doesn't look too bad. Canada has some narrowing, but many other countries are worse
https://www.cia.gov/the-world-factb...c697718037/NorthAmericaPopulationPyramids.jpg
This is a nice site with many population pyramids in the same place
Population Pyramids by Region - The World Factbook