I don't think this is true. I checked the stats for caloric supply and the highest value worldwide is (unsurprisingly) in North America where about 3,500 calories of food are produced per day. That is less than double what a person needs per day, so "several times" seems unlikely.

But I don't dispute the idea that we produce enough food to feed the world. But I also didn't say we didn't.

Could you comment on what I actually said, which is that an ageing population (or any situation in which there are more non-workers per worker) will result in less production being available for people on average?

This is not just about food; it is also about other necessities (such as healthcare) but also non-essentials like entertainment. The problem of an ageing population is not that we'll starve to death; it's that our quality of life will decrease.

At the end of 20 years a child becomes an adult, who will (on average) be a net producer. It's true that children cost more in work put into raising them than older adults take in work to look after them, yet it is a fact of life that one working human is capable of producing more stuff than just that which they themselves needs or makes use of - otherwise it would be impossible to raise children. This should be obvious, and means that the problem of an increasing birth rate, from this perspective, is at most temporary.

But I didn't say we should have high birth rates, I said that the problems of low birth rates are not due to capitalism.

I can't really connect this comment with what you originally said. Maybe this will help clarify my position: I think countries with public health and social care, just like countries with mainly private health and social care, will have severe problems if they can't arrest the rate at which their populations are ageing. My comment explains in very general terms why I think that is the case.

You do know that corporate profits are literally where old people get their money, right?

Take the posterchild of capitalism as an example, the US. People over 55 own 52% of all assets, from money to homes to companies. As a group they outweigh the billionaire class about 8 to 1 by wealth (and of course most billionaires are themselves also old). That's how retirement investments work, you live off the backs of young people who work.

Get rid of capitalism, you just get a different way to route young people's productivity to old people. Hell, get rid of currency and it doesn't change. Everyone's producing food and goods, but a large share of it goes to people who are old and no longer work. The larger the share of people not working, the larger the burden on the people not working.

Unless the population is constantly growing, retirement is a burden on young people regardless of economic system.

Nothing I said related to capitalism at all as far as I can see, so you're going to have to connect the dots for me if you want me to understand, sorry.

The tricky part of being in society is that we want systems that work for more than just ourselves: It's not a purely transactional relationship.

Great news! It doesn't affect you either way, so we know your opinion on the matter is completely unbiased. That's excellent.