The global demographic transition presents marked asymmetries as poor, emerging, and advanced countries are undergoing different stages of transition. Emerging countries are demographically younger than advanced economies. This youth is favorable to growth and generates a demographic dividend. However, the future of emerging economies will bring a decline in the working-age share and a rise in the older population, as is the case in today's developed world. Hence, developing countries must get rich before getting old, while advanced economies must try not to become poorer as they age....