Altho now that you think about it, he is not really a citizen, he has a SS #, was allowed into the military, etc and they never caught it? Clearly there are problems with the system.
I hope you do realize that in 1916 people weren't obsessed with paperwork, databases, and forms like they are now.
A family bible was just as good as a birth certificate, people were born at home, and we had open immigration at the time. States didn't have drivers licenses and your identification was the name that came out of your mouth.