Why do demographers talk about economics? They're complete illiterates on the subject. I've yet to see one of them understand the equation GDP = size of the labour force * productivity.
To them, GDP = number of people between 16 and 64.
I'm going to make a statement that's going to boggle the demographer's mind: China's labour force is expanding and will continue to do so for the next quarter century. I want to thank whoever posted that graph of Chinese agricultural labour because it illustrates my point perfectly. The people employed in agriculture above ~5% of the population are wasted, they don't even count. These are subsistence farmers, they contribute nothing to China's national economy beyond keeping themselves alive. That's a population of 280 million people whose contribution is zero.
That isn't part of the "labour force." The engineers at CASC working on Chinese rockets and missiles are part of the labour force. The engineers at Huawei working on 5G and 6G telecommunications technology are part of the labour force. You get the idea. Farmer Zhang hunching over all day in a rice paddy because he's too poor to afford machinery and China's agricultural sector is too backward isn't part of the labour force. If there's a machine out there that can do your job, you aren't contributing to the economy. You're just wasted effort.
Thankfully, every year around 14 million Chinese leave miserable existences like Farmer Zhang's and migrate to the cities. True, the jobs they get delivering food for Meituan suck, but they're contributing to the national economy. Much more importantly, their children (yes, they have them) are being properly educated and are going to get STEM jobs at companies like Huawei and CASC.