As Andrew Yang has pointed out, GDP is a pretty poor measurement, and at least in China's case, not transparent and most likely inflated by localities self-reporting to meet central government targets.
GDP is proportional to population, so if you have a larger population, your GDP can be proportionately larger. The question is, what's GDP per capita or GDP per capita PPP? China per capita GDP is 1/7th-1/8th of the US, and India per capita GDP is 1/30th of the US, will they make it up in 10 years? China could, if they can keep up their growth and not experience a major recession or depression, which seems unlikely.
GDP is proportional to population, so if you have a larger population, your GDP can be proportionately larger. The question is, what's GDP per capita or GDP per capita PPP? China per capita GDP is 1/7th-1/8th of the US, and India per capita GDP is 1/30th of the US, will they make it up in 10 years? China could, if they can keep up their growth and not experience a major recession or depression, which seems unlikely.