How can people think that China's is the world's next superpower?

In China, the age at which men retire is 60. It's five or ten years earlier for women. This might have worked well in the past, but with China's low fertility rates for decades and decades, their population is now becoming dramatically top-heavy.

By 2050, China is projected to have 43% of it's adult population over the age of 60, outside of the working age.

With this trajectory, it seems like China's workforce growth will expire in a decade or so, and then start plummeting by around 8M per year. What then? How will they deal with a population that is primarily elderly people? Won't the loss in productivity and the consumption from the elderly make a serious dent in the leftover wealth that would pay for having children?

I don't see how they can possibly get out of this hole that they've dug themselves into and become a world power, even if they do have huge gold supplies.