Walter Matthau was 32 in Atomic Attack when he played the character 'Dr. Spinelli'.
That was over 70 years ago in 1954.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
In 2000 he died aged 79, starring in 85 films in his career, 84 of those after Atomic Attack was first released. If he were alive today he would be 103.
In Atomic Attack, I think Walter Matthau looks: