Well, they had a unique one-child policy for over three decades, and are only now starting to feel the ramifications.

In China, the children are expected to take care of their parents in their twilight years, and the husband is typically expected to provide for the wife and kid(s), so you basically have 1 dude providing for 8 people: himself + his wife + 2 kids + his parents + his wife's parents.

Any way you cut it, China is due for ~35 years of an absolutely horrendous labor participation rate. And unlike developed nations with declining birthrates, it's unlikely immigrants will be able to take up the slack, as extreme xenophobia is omnipresent in China and her population is absolutely massive.

To be fair to the post you're replying to China's demographic issues are more pronounced and likely to occur much sooner than most other large economies. The biggest issue being that they have never normalized immigration when they needed to like many western economies started to do in the 70s.

No, it's an issue in many countries. You will note, however, that this post regards China and India, and my comment was a comparison between the two. Pay attention.