Without immigrants with many children, we would have long since become over-aged here in Germany. Of course, I don't know if that's enough. The question would be "what will it be enough for? I assume, for tax revenues due to gainful employment. Since old people are no longer working, other ways will be found to keep markets stable. More taxes on consumer goods and wealth and pensions will follow. Homeowners are already taxed more. The government takes from everywhere it can. The vaccination campaigns have brought in profits galore and I think the human body itself will be (and has been) released for exploitation to compensate for the lack of tax revenue. Where natural markets can no longer be developed (due to material resource shortages or artificially created ones), they are invented or mentally staged. Cynically, one could ask how much an over-aged population can financially serve the whole in order to replace the missing labour force. Other sources say that labour is the last bulwark against exploitative intentions. But if human labour is predominantly done by machines, the human being no longer has any leverage in this respect (resignation, strike, etc.). I doubt whether automation has really progressed that far (and I don't know when it will).
According to my subjective observation, there is clearly childlessness. You only have to recall the street scene of your own childhood and compare it with today. I also agree with the prediction that the child-rich civilisations hitherto described as developing countries are tending towards child poverty. This trend seems unstoppable to me.
This really did a number on Japan.
Is Japan an example of an over aged population par excellence? How would one know?