China's stunning economic growth over the past 30 years has been fuelled by the sweat of a generation of workers at the peak of their powers. As a result, China's economy is on-track to overtake the United States by 2030. With an average growth rate of more than 9 percent between 1980 and 2010, China became the world's second-largest economy in 2010. But now a demographic reversal unlike anything since the great famine in 1959-61 casts doubt on this prosperity. A rapidly ageing population and declining fertility are set to plant a bomb under the economic boom. Since the 1950s,…