Aitcheson feels like he was destined to be a hockey player. One year he got skates for Christmas, which were put on him by his grandparents. Then he looked down at them and told his grandfather, "I need ice."

Aitcheson's path began at Ted Reeve Community Arena in the Scarborough section of Toronto and led him to the 2025 NHL Draft, where he was selected by the New York Islanders with the No. 17 pick. He signed a three-year, entry-level contract with the Islanders on March 17, 2026, when the Barrie captain led all Ontario Hockey League defensemen in goals (28), power-play goals (15), points (70) and plus/minus rating (plus-45) through 54 games. He also played for bronze-medal winning Canada at the 2025 IIHF World Junior Championship, where he had one goal and three assists in seven games.

He ended his draft-eligible season third among OHL defensemen with 26 goals and seventh with 59 points (26 goals, 33 assists) and 21 power-play points (nine goals, 12 assists) in 64 regular-season games for Barrie. He tied for fifth in playoff scoring by a defenseman with 12 points (six goals, six assists) in 16 games, and was praised for being fierce and getting in the face of his opponents. His 88 penalty minutes ranked second on Barrie during the 2024-25 season.

Aitcheson began to stand out among NHL scouts with his blend of offensive touch and physicality during the 2024 CHL/Top Prospects Challenge. That carried throughout the season to where he was No. 9 in NHL Central Scouting's final ranking of North American skaters, up from No. 15 in the midterm rankings in January.