Look at the UN World Population Projections. These are updated regularly. They contain the verified data from 1950 to the year of the update and the projection through to 2100 using a high, medium and low variant growth model. Under both the medium and low growth model China will begin losing population from 2025. The workforce began shrinking in 2011 (official China data) and the absolute population is expected to shrink from 2025. Beside the UN pop data, you could also check out my new book The Chinese Economy out next month in the UK with Agenda Publishing that discusses the implications of the shrinking workforce and ageing for productivity and in turn the prospects for China being able to foster the innovation necessary to raise productivity levels in order to realise its goals for 2049 of being a wealthy and strong country (fuqiang guo).