Comparisons:
- https://www.populationpyramid.net/africa/2020/
- https://www.populationpyramid.net/asia/2020/
- https://www.populationpyramid.net/europe/2020/
(Northern America is still growing: https://www.populationpyramid.net/northern-america/2020/)
https://worldpopulationreview.com/countries/china-population
Focusing on Africa isn't arbitrary. They are where the majority of future human population growth will be coming from.
I would think that, in aging populations, many of the jobs most difficult to fulfill by count would be in service jobs (care homes, nursing, Uber eats cyclists, bus drivers, etc)
There likely will be millions of people in Africa willing to take on such a job and capable of doing so.
Also, chances will be higher that those people would want to emigrate than, say, Chinese nurses, as there will already be plenty of demand in China.
They also seem to lack the basic mathematical notion that one doesn’t add things that are different in nature: “on additionne pas des choux et des carottes”. For them a population size is a population size with no thought given to the underlying composition of the population.
Which is the main reason all their mental models on this particular topic are often so wrong in practice