Robertson, 20, totaled 90 points (36 goals, 54 assists) in 68 regular-season games with the Peterborough Petes of the Ontario Hockey League (OHL), setting OHL career highs in assists, points, power-play goals (13) and game-winning goals (nine). He led the Petes and tied for 11th in the OHL in scoring in 2022-23, and ranked in the top five on his team in goals (second), assists (first), power-play goals (second) and shorthanded goals (three, tied for second). Robertson topped all OHL skaters with 831 faceoff wins and his 58.5 percent success rate at the faceoff dot in was the best mark among OHL skaters to take at least 1300 draws. Robertson recorded an OHL career-best 22 points (nine goals, 13 assists) in 23 playoff games en route to winning the OHL Championship with Peterborough. He finished the postseason ranked in the top 10 in the OHL in playoff goals (tied for seventh), assists (tied for eighth), points (tied for eighth) and game-winning goals (three, tied for first).