Although the book Shaddam IV is described a a trim figure seen only in military garb, a redhead in his 70s, while appearing no older than middle thirties, I personally think casting Walken was probably a great move.
A minor rant about the eyes- “a touch of the blue” is an insult to the slightly-possibly addicted, while the Fremen, eventually including Paul, all have the deep blue-within-blue with no visible irises. The Spacing Guild navigator has such an addition that the eyes are almost black, they are so blue.