I know "Free, White and 21" is the name of a movie produced in 1960s. However, the above words have been used in "1919" by John Dos Passos published in 1930s:
Please tell me if those words have a diffrent story beyond their meaning.Eveline looked at herself in the mirror before she started dressing. She had shadows under her eyes and faint beginnings of crowsfeet. Chillier than the damp Paris room came the thought of growing old...
"How old are you, Paul?" she asked him when she came out of her bedroom all dressed, smiling, feeling that she was looking her best.
"Free, white and twenty one..."