Mark Goddard was born July 24, 1936, so he was 29 on Sept. 15, 1965, when the series premiered.
Major Donald West
His given name is Donald and he is a graduate student studying radio astronomy (No Place to Hide).
He is an officer in the US Space Corps (The Reluctant Stowaway).
He is an excellent cook.
He once studied to be an architect (The Flaming Planet).