The trend varies widely – with some nations aging rapidly while others remain demographically "young." In a report issued by the Center for Strategic and International Studies in Washington, Mr. Howe and coauthor Richard Jackson have warned that this demographic divergence could be a source of geopolitical instability during the 2020s. (Countries with looming "youth bulges" and high potential for civil unrest include Afghanistan, Iraq, the Palestinian territories, Somalia, Sudan, and Yemen.)
Other nations could face financial burdens and political tensions because of a different problem: a rapid decrease in young people. Russia is already becoming an extreme case of outright population decline. Other nations that could soon experience falling populations include South Korea (around 2020) and China (by about 2030).
If Asia will host the biggest gains in the number of people over 65, Europe can claim the title of being the furthest along in "aging." It will have just two working-age people for each person over 65 by midcentury, the United Nations predicts (compared with a 4-to-1 ratio in Asia).