Robert Mitchum was 24 in To the People of the United States when he played the character 'Bomber Ground Crew (uncredited)'.
That was over 81 years ago in 1943.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
In 1997 he died aged 79, starring in 139 films in his career, 138 of those after To the People of the United States was first released. If he were alive today he would be 106.
In To the People of the United States, I think Robert Mitchum looks: