China's workforce is already shrinking and yet their population is still rising, all thanks to the 1 child policy, which also led to the demographic imbalance mentioned.
Historically, when you have a lot of men who have no chance at getting married, it leads to all kinds of social unrest. When you have 33 million of them, well, its going to get ugly.
Plus the shrinking workforce is going to bite hard very soon - it won't be long until there are just 2 workers having to provide for each retiree. And that is just retirees - it doesn't count children, public servants, the army etc.
China's economy is going o crash hard when that hits.