The problem in China is that they're likely to get old before they get rich. China's GDP per capita is still only a quarter (or less) of Japan, Singapore or South Korea:
If you look at cities like Shanghai, Nanjing or Beijing, there's a subtantial minority already basically living with western living standards. That number is still growing quickly.
Furthermore, China has little problem letting old people work longer - or potentially even implement pretty brutal policies regarding the elderly.
So while China is growing old very quickly, and this will slow down progress, I do not believe it will lead to a halting of progress.
I would be concerned about China in the 2030s and 2040s.
But I bet you already knew all that.
If the experts are correct, can they hurry up and be correct faster because I can't wait for a prediction that has no timeframe requirements.