[2] Born in Boston, Mason batted left-handed, threw right-handed, and was listed as 5 feet 11 inches (1.80 m) tall and 160 pounds (73 kg).

He graduated from Newton High School, where he was a standout in baseball and hockey,[1] and attended Parsons College before signing with the Washington Senators in 1965.

That year, Mason hit 18 home runs and batted .285 in the full-season Class A New York–Penn League and was selected by the Giants in the winter Rule 5 draft.

One of those hits was his first big-league home run, a solo blast off Sammy Ellis of the Cincinnati Reds on June 24.

All told, Mason collected 143 hits, with 16 doubles, three triples, three homers and 27 runs batted in in 336 big-league games.