There's also the fact that China is cheating by artificially keeping their currency low.  That will eventually come back and bite them in their butts.

I am not exactly sure about their practices but additionally, one needs to look into the share of consumption in the economy. We don't typically do this, as the shares usually do not change as much between countries (or at least stable over time) but Chinese economy is an ANOMALY. What do I mean by that?....

Now, the well being of people is not measured in income but CONSUMPTION, and for example, if you are investing most of your income, and there is hardly anything left to consume, then you may LOOK wealthy but you are actually MISERABLE. In US, the share of consumption is 70% whereas it is measly 35% in China. This means, whatever number you see in Chinese GDP/cap PPP, the Chinese actually end up spending only 35% of it.

Let me give you an example....

GDP-PPP(2013), from IMF

US : $ 53.001

Consumption share : $37100

China : $ $11.868

Consumption share : $4.154

So the difference is much larger than it appears...

It's worth pointing out that this is in large part due to China's population, which is roughly four times that of the United States. Population can skew total GDP in a more populous nation's favor (e.g., Nigeria's GPD is larger than Norway's, but only because its population is about 35 times larger). In terms of raw 2013 GDP numbers from the IMF, the U.S.'s GDP was $16.77 trillion while China's was $9.47 trillion. But the population difference makes China's per capita GDP far lower than that of the U.S. America's per capita GDP is about $53,000 while China's is a mere $7000. Even in PPP terms, which is the focus of the article, China's per capita GDP is less than a quarter that of the U.S.

All other things being equal, if China had the same population as the U.S., their GDP would be about a quarter of what it is and they'd end up dropping to 7th place in raw GDP numbers, right in between the UK and Brazil. Conversely, if their per capita GDP were the same as the U.S., their total GDP would be four times that of the U.S.; if every other country's GDP remained the same, that would result in China generating half of the global GDP. China's population is stabilizing, but assuming they're able to keep growing their economy it would have to be through increasing the per capita GDP. But there are likely some serious obstacles to indefinite economic growth, not just for China but any nation, including resources needed to provide sufficient energy, good jobs, and a good standard of living for everyone, but in China's case especially authoritarian regimes almost never have truly advanced economies, certain extremely oil-rich nations like Saudi Arabia, Qatar, and the UAE being exceptions as said resource generates the vast majority of their GDP (if the rest of the world could and did ditch oil entirely tomorrow, it would cripple the economies of OPEC nations). It's probably no coincidence that OECD nations and nations listed as "advanced economies" by the IMF (both groups with significant membership overlap) are all multiparty electoral democracies. Before its dissolution the Soviet Union had the second-largest economy in the world in terms of total GDP, but its per capita GDP was something like a third that of the U.S. Assuming they have the resources needed and having an authoritarian single-party government doesn't prove to be an obstacle (or they democratize), then it's possible that China can keep narrowing the per capita GDP, but I think a good argument can be made that their current growth is unsustainable given current conditions. I don't think anyone can realistically expect any nation to indefinitely experience double-digit GDP growth every year. There are always limits to growth.

So, while China's GDP is large, it's not because they are as well-off as America economically. It's because there's over 1.3 billion people in China. In essentially every way that counts the U.S. is better off. The UN's Human Development Index ranks the U.S. at #5 while China is only at #91. 27% of Chinese people are living on less than $2 per day according to the World Bank, while in the U.S. it's a negligible amount. According to the World Bank the market capitalization of listed companies in the U.S. is five times larger. Even in terms that aren't purely economic, the U.S. is better off. Americans live longer and healthier. China is increasingly more polluted, with more deaths per capita from air pollution (Because who cares about clean air when you have an economy to grow? I doubt the CPC does.). China is a single-party authoritarian state, while the U.S. is a multi-party democracy; the Freedom House report gives America top ratings for political and civil rights, while China has consistently received very poor ratings. According to Corruption Perceptions Index, America's government ranks 19th least corrupt among 177 nations, while China only ranks #80. It's quite clear that the U.S. simply has a better overall economy, standard of living, and quality of life than China. China has a long way to go before they join the ranks of developed nations like the U.S., Japan, and the member states of the EU.