The world is growing older but it is not growing older evenly. In many advanced economies, birthrates have fallen to historic lows, populations are aging rapidly and employers are struggling to find enough workers. Meanwhile, across much of Africa, South Asia and parts of the Middle East, millions of young people enter the labor market every year with aspirations that far exceed the opportunities available to them at home. The result is the defining demographic conundrum of the 21st century: Aging societies need workers, while younger societies need jobs.