["Review of Development Economics, EarlyView. ", "\nABSTRACT\nWhether favorable population structures can be translated into sustained demographic dividends remains uncertain and context dependent. Using panel data for BRICS from 1990 to 2022, this study develops a demographic–economic dual system framework to examine how population opportunity and economic conditions jointly shape demographic dividend outcomes. We construct a composite Demographic Dividend Index (DDI) using a combined CRITIC–entropy weighting method. The results reveal substantial cross‐country heterogeneity and dynamic adjustment patterns. China and Brazil maintain relatively high demographic dividends despite population aging, reflecting strong economic absorption capacity, whereas India fails to fully realize its demographic potential due to persistent labor market constraints. Russia's recent improvement appears policy‐driven and fragile, while South Africa remains trapped in a low‐level demographic–economic equilibrium. A typological analysis further identifies distinct transition paths and sustainability challenges across countries. Overall, the findings indicate that demographic dividends are conditional on economic structure and policy coordination, underscoring the importance of targeted labor market, industrial, and human capital policies in emerging economies.\n"]