The issue he is referring to is the 'age cliff'. When one child came in, the proportion of children to workers suddenly dropped. That was very useful for produ

The issue he is referring to is the 'age cliff'. When one child came in, the proportion of children to workers suddenly dropped. That was very useful for productivity, as people were working not caring for children. The other side of that coin is the age cliff. This is not a decline in population, so much as a change in the proportion of workers to old people. Note that because of the nature of work, 50 year olds in China are often at the end of their practical working life, because the work is hard and they are disabled. The problem is similar to the baby boomers in America, suddenly, a smaller number of workers must support larger number of non-working old. However, it is much worse because the shift in birth rates was much sharper. This is a problem for the next decade or so. However, like all these things, it does not necessarily mean the apocalypse. China has built up great wealth and interests overseas, and the government (which will end up carrying much of this cost) controls many of these interests. You would be looking at a shift from an economy that primarily produces, to an economy that primarily consumes, like the US.