Howard French has a fantastic piece on Chinese demographic trends over at the Atlantic. Consider this:

China today boasts roughly five workers for every retiree. By 2040, this highly desirable ratio will have collapsed to about 1.6 to 1. From the start of this century to its midway point, the median age in China will go from under 30 to about 46, making China one of the older societies in the world. At the same time, the number of Chinese older than 65 is expected to rise from roughly 100 million in 2005 to more than 329 million in 2050—more than the combined populations of Germany, Japan, France, and Britain.

And here is a summary of global population projections for perspective: