First, the size of the population of youth in comparison to the size of the adult population is determined, whether it becomes evident that the majority of nations have high or very high numbers of youth relative to adults. Second, the opportunities nations provide their young people are evaluated by looking at the range and average levels of economic, political, social, and educational development within the modern world system. Third, a strong relationship is found between relative size of the youth population and national development, with youth ratios most closely associated with educational and political development. The results of this study demonstrate the existence of inter-age and intra-age stratification throughout the world, which has important implications for the future well-being of youth as well as the world system of nation-states. (Author abstract)