2011-12: Alex Peters appeared in three midget major games (including two playoff contests) with the Huron Perth Lakers in Ontario; spending most of the season with the club's midget minor team. He had no points and 2 penalty minutes with the midget major squad. In 28 midget minor regular season games he scored 8 goals with 5 assists and had 14 penalty minutes. Peters scored 3 goals with 2 assists and 6 penalty minutes in eight playoff games. Competing for Huron Perth in the OHL Cup he had 2 assists in four games. The Plymouth Whalers selected Peters in the second round (33rd overall) of the 2012 OHL Priority Draft.
2012-13: Peters, whose older brothers Justin Peters (CAR) and Anthony Peters were both OHL goalies, skated for Plymouth as a 16-year-old. He had 12 assists and was +9 with 31 penalty minutes in 58 games for the Whalers during the regular season. Plymouth finished first in the West Division and reached the conference finals against OHL champion London. Peters skated in 13 playoff games; finishing +4 with 1 assist and 11 penalty minutes.
2013-14: Peters returned to Plymouth for his second OHL season with the Whalers. He was selected to play for Team Orr in the 2014 CHL/NHL Top Prospects Game.