I think it is mostly the education of women that lowers birth rates, and that only occurs in prosperous countries.
I also thought that escorting economies into the 1st World caused parents to only have one or two children, since now there was a hope for their future that encouraged an investment in resources (like education) that could only be done with a smaller family (although I have heard of the successes of microfinancing done with women in Africa.)
There's also a catch to population aging and lower birth rates: businesses want more sales each time, which means more consumers, and older people need younger ones to care for them.
I think the higher-level issue is that lots of governments are hooked on GDP "growth." Rather than being a measure of the economy, it has become an end unto itself...a "goal" if you will. There's nothing wrong with contraction, if it is proportional to the population. And this aging population imbalance is putting strain on a lot of countries...but it's self-correcting. You just gotta be patient.
I can't remember anymore, but I think the World Bank pointed out that that GDP per annum increase has to be at least three times higher than population growth to account for inflation and to offer a buffer in the event of a disaster like a war or a pandemic. And even as birth rates are lower, societies are more expensive to maintain due to more advanced infrastructure, greater demand for energy and resources from the populace as it attains middle class status, and competition from other countries. Thus, the pressure to earn and to show the voting public that they are working increases.
Inflation is and has been caused by the Federal Reserve inflating and deflating the value of the dollar since the inception of that consortium of private banks. It has taken the value of the dollar to basically zero and now we and all countries with central banks are wondering what we will do. Your house is not worth three times its value from 20 years ago. The dollar is worth three times less.
I read somewhere that the Fed was patterned after the Deutschebank of that period and was designed to fail after about a century, but it would many in the upper echelons wealthy in the process at the expense of the commoners. Germany had their collapse during the Weimar Republic and we are having ours now.
There's also the issue of diminishing returns, such that cost in terms of energy is rising. For example, we used to be able to extract a hundred barrels of oil using the equivalent of only one barrel. Now, it's down to around three. The reason is physical limitations of the planet: the need increasing amounts of energy to get oil that's deeper and we more energy to refine it because it's dirtier. It's similar for minerals: we need heavy equipment to move increasing amounts of earth to get less copper that's also of lower grade. Meanwhile, we need more oil, copper, etc., because we've moved from horse-drawn carriages to cars.
All parts of the industry are making more money than ever. Why should they increase production or change anything else? Perhaps I've missed it, but but have we driven less because of it? I haven't.
Money is a very deceptive thing because it is essentially a promissory note. The actual wealth of the global economy consists of material resources and energy available which are needed to produce the goods and services that that money can buy, and they are constrained by the physical limitations of the biosphere.