Prior to turning professional, Gettinger played four seasons with the Sault Ste. Marie Greyhounds of the Ontario Hockey League from 2014-18. He was named to the OHL First All-Rookie Team in 2014-15 after recording 25 points, a plus-10 rating and 13 penalty minutes in 54 regular-season games. In total, Gettinger compiled 187 points (91-96-187), a plus-67 rating and 125 penalty minutes in 242 OHL games, along with 35 points (13-22-35) in 53 playoff matchups. The Cleveland, Ohio, native also spent time with the U.S. National Team Development Program, netting two goals and six penalty minutes in four appearances with the under-17 team during the 2014-15 season. On the international stage, Gettinger played for Team USA at the 2015 Ivan Hlinka Memorial Tournament, showing four points (2-2-4) and 30 penalty minutes in four games.