Or, women marrying up. From the Economist:
This habit of hypergamy (ie, marrying a person of higher social station) is documented in a recent Master's thesis by Yue Qian, a PhD candidate at Ohio State University. Although most Chinese newlyweds, like couples everywhere else, are of similar age and education, it is quite common for Chinese women to marry men who are better educated than themselves. As a corollary, men often marry women who are less educated. According to Yue Qian's calculations, 55% of university-educated Chinese men marry a less educated spouse, whereas only 32% of university-educated women do the same.
... But although numbers are on Chinese women's side, time is not. Women's marriage rates drop steeply after they turn 30 (see the chart below adapted from Yue Qian's thesis), something that is much less true for men. One explanation for this is hypergamy of a different kind: older husbands often take younger wives, but older women rarely marry younger men. The odds of a man marrying a younger spouse are almost 50 times as high as the odds of a woman doing so, according to Yue Qian. This "age hypergamy" has uneven effects on women's marital prospects. It improves the chances of younger women even further: they have plenty of men their own age to go around and they can also marry older men as well. But it hurts the chances of older women, who must compete with younger rivals for men their own age.
The upshot is that first marriage rates for young women are much higher than for young men. But unmarried women in their thirties are less likely to marry than thirtysomething men, despite being outnumbered by them (see chart). Women, especially "A-quality" women, who do not marry early often do not marry at all. Indeed, women over 30 who boast a university education have even lower marriages rates than poorly educated, similarly aged men who lack a high-school education.
There is an opinion that A quality guys will find B quality women, B quality guys will find C quality women, and C quality men will find D quality women...The people left are A quality women and D quality men.