There is a popular notion that a country can "breed itself" out of the aging population "problem". On one level it makes sense: population aging is largely caused by a decline in the birth rate. Increasing the birth rate, by definition, should alleviate the "problem".

In 2015 China had about 930 million people aged between 20 and 64 compared to 131 million aged above 65. And by 2050, the population of people above 65 is likely to be about 370 million. In order to maintain the 2015 ratio, the "working age population" would need to be 2.65 billion. Even to have half of the forecast increase in the ratio, China would need a working age population of more than 1.5 billion.

So what does this mean for the birth rate? It means that to have the 2015 dependency ratio in 2050, there should be more than 127 million extra births a year. This scenario is made even more remarkable by the fact that the number of women aged between 20 and 40 is forecast to decline from 207 million in 2015 to just 134 million in 2050.