It really shouldn't be surprising that after a few decades of one-child policy you're going to wind up with far more old people than young people. If they didn't see this one coming then I'd be very surprised.
Most Western countries are facing a similar problem with aging populations, though on a lesser scale demographically. On the other hand, the Chinese government is much happier to leave folks to fend for themselves, while Western governments run into problems as the old folks demand ever-increasing spending on pensions and health care.
It has been known for at least a decade. I had some resource on this but they went bye-bye along with my hard drive. I'll see if I can find them and edit this post.
Most Western countries are facing a similar problem with aging populations, though on a lesser scale demographically. On the other hand, the Chinese government is much happier to leave folks to fend for themselves, while Western governments run into problems as the old folks demand ever-increasing spending on pensions and health care.