BSD,
According to US Census,
http://www.census.gov/compendia/statab/2012/tables/12s0080.pdf
there are 105 males born for every 100 females. If this is also true for the Jewish population, we would expect that even with a small age gap (with the boys slightly older than the girls), there might still be more boys than girls.
In a previous thread, this statistic was used by one poster to erroneously disprove the age gap theory. He was wrong, because the yeshivish age gap is too wide, but the point has some merit.
real-brisker,
Not likely, but you never know.