Mox, the problem with looking at the average is that you miss part of the story. Even though AZ will not admit to it, trying to marry off people of similiar ages either means women will get married later or men earlier. There is no way around that. That is asking a big sacrifice for men or women, if its not certain it will help. I showed in quite a few years that making the age gap smaller does NOT alleviate anything. All you are doing is delaying women from getting married by two years, which is unfair.
As to the growth rate – there is a much greater mortality rate for boys than girls. According to what I read on the CDC and other sites,by late teens/early 20s, the population evens out to be approximately a 1:1 ratio.