Stanley Kubrick was 18 in Dreams That Money Can Buy when he played the character 'Theatre extra (Uncredited)'.
That was over 77 years ago in 1947.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
In 1999 he died aged 70, starring in 17 films in his career, 15 of those after Dreams That Money Can Buy was first released. If he were alive today he would be 95.
In Dreams That Money Can Buy, I think Stanley Kubrick looks: