China's repaying of the demographic dividend

Today the Wall St. Journal relays a report by Citigroup analysts claiming that population aging brought on by the one child policy in China could reduce annual growth by 3.25 percentage points between now and 2030. I haven't had time to verify this, but that seems like an enormous effect. But then again, fertility in China has indeed fallen a lot, from a TFR of 2.5 births per woman in 1990 to 1.7 in 2011 according to the World Bank's WDI database.