When did they talk about younger boys joining to army

This happens in chapter 1. Union soldiers gathered at the Flint courthouse, anxious to go off to war. They were certain that the conflict would last less than three weeks. Emma Edmonds was in the line of young soldiers. She pulled her cap down low on her forehead, hoping that she wouldn't be discovered. She was used to men's clothing—that's what she had worn on her family farm in Canada for many years. Now at twenty-one, her slim and boyish figure and short cropped hair did not set her apart from the young men in line. The Union Army was so desperate for able-bodied men that they were foregoing physical exams. Still, Emma was nervous about being exposed.