The RI Cemetery database estimates his birth year as 1708, but his parents weren't married at that time. Perhaps the age on the gravestone is incorrect or was misread.
William's will mentions his father, Elisha, wife Phebe, and children: Job, William, Thomas, Ann (w/o Capt. John Ladd), Phebe (w/o Samuel Hopkins), & Mercy; also his aunt Catherine Brown. I think she must have been Catherine (Greene) Brown, wife of James and sister of Anne Greene, who was mother of William's wife Phebe.
William & Phebe are buried in the Arnold Lot, formerly the Old Baptist Church Cemetery, on the south side of Cowesett Rd., directly east of the Elms Apts., about 40 ft. up on the hill.
Abt 1710 - 1786 (76 years)