Deborah Kerr was 18 in Major Barbara when she played the character 'Jenny Hill'.
That was over 83 years ago in 1941.
This was her first recorded movie acting credit (although may not technically be her first actual acting role).
In 2007 she died aged 86, starring in 59 films in her career, 58 of those after Major Barbara was first released. If she were alive today she would be 102.
In Major Barbara, I think Deborah Kerr looks: