 McGah attended Roosevelt High School in Oakland, and after graduating was signed by a Red Sox scout.McGah first played in the Boston minor league system in 1940, with the Canton Terriers of the Class C Middle Atlantic League; his season was cut short by a knee injury.In 1941 he began the season with the Oneonta Indians of the Class C Canadian–American League, then moved up to the Scranton Red Sox of the Class A Eastern League.