Benedict was Governor of Rhode Island 1663-66, 1669-72, and 1677-78.
From "Early Records of the Arnold Family" in The New England Historical and Genealogical Register: "We came from Providence with our family to Dwell at Newport in Rhode Island the 19th of November, Thursday in afternoon, & arrived ye same night. Ano. Domina 1651. . . my father and his family Sett Sayle from Dartmouth in Old England, the first of May, friday & Arrived In New England. June 24th Ano 1635. We came to Providence to Dwell the 20th of April, 1636. per me Bennedict Arnold."
So, Benedict was 19 1/2 years old when he came to America with his family.