A minor point that may have some relevance here. When I was doing genealogical research on my great grandfather who served in the US Civil War, I read that at the time, your legal age was considered to be the age you would attain by the end of the calendar year, so everyone officially aged up on January 1. By this convention, many 17 year-olds who enlisted would have been legally 18 and did not actually lie about their age.