Christopher Plummer was 27 in Little Moon of Alban when he played the character 'Kenneth Boyd'.
That was over 66 years ago in 1958.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
In 2021 he died aged 91, starring in 176 films in his career, 175 of those after Little Moon of Alban was first released. If he were alive today he would be 94.
In Little Moon of Alban, I think Christopher Plummer looks: