Human population and the future of the world

Population numbers and age distributions today are vastly different than they were fifty years ago. Most dramatically, people today have longer lives and fewer children than their grandparents or even their parents. Why does population matter? Firstly, the age distribution of a country shapes factors such as labor supply, costs for care of the old, and vulnerability to diseases such as Covid-19. And secondly, population numbers and trends determine (in important part) the pathways to global prosperity, such as the demands for food and energy.