The study found that China has 119 male births for every 100 girls, compared with 107 to 100 for industrialized countries. . . . Ratios in Jiangxi and Henan provinces were the highest in the country, with 140 boys for every 100 girls in the 1-4 age range[.]
Boys tend to die prematurely more often than girls, so the slight imbalance that is natural tends to even out by adulthood. In old age, women now greatly outnumber men, something that large numbers of death in childbirth prevented in earlier eras. Negative conseqeuences have been predicted, but it is hard to tell how accurate those predictions will be.
War has led to excess numbers of women historically on multiple occassions. Prisons and remote work sites (like the mining towns of the early American West and military garrisons) have seen excess numbers of young men. But, there are few, if any, historical cases that I am aware of, where a whole generation of a huge nation like China have had a surplus of young men.