Some of them are still in their seventies, I believe. I heard that one vet went to war in 1943 (IIRC) as an eighteen or nineteen year old.
Elgin WW II Veteran Given Overdue Medals
Courier News
By Anne Marie Apollo
In 1942, at the age of 16, Schnulle lied about his age so he could enter the armed forces. He served in California and later on Iwo Jima, the site of some of the fiercest fighting in World War II. He also served in Hawaii. When the war ended, he completed his tour of duty in Japan.
I am sure that there were younger men than this, but we may never know, because the DD 214 was used to prove age, therefore voting and of course retirement.
I myself joined the National Guard when I was 15, in 1954. I did correct it with Social Security as they had it wrong in any case, off by 4 year. According to my Birth Certificate, which almost no one I new had.
They would take your word, or an entry in a family Bible, then finally all the hand written birth certificates finally made it to the state archives. Only my younger sister was born in a hospital, rest of us had to make it on our own.