Birth control (and one of its consequences, older population) are unfortunately only one side of the coin. Interestingly, Mother Nature "regulates" the population in a way that in peaceful times 51 to 52 percent women are born but at the war time, more male babies are born.

http://www.popsci.com/scitech/article/2008-12/why-does-war-b...

I suppose, the same (proportion of ~ 51:49) would happen in China despite birth control. The real problem is "Female Infanticide", due to bias in many "patriarchal" societies towards women as being somewhat inferior to men.