Everything changes. Though all countries age, within four decades the U.S. will likely have one of the lowest percentages of elderly citizens, and one of the highest rates of working-age bodies among large economies. China, meanwhile, will see its working-age population plunge and its elderly ranks soar — an echo of its one-child policy. Europe falls deeper into age-based stagnation. Alas, Japan becomes the global equivalent of Boca Raton. (Note: I excluded India from the list because it has a low life expectancy, which skews the comparison.) (via The Most Important Numbers of the Next Half-Century)