Boelius started playing ice hockey at the age of four with
HC Ässät Pori. He played as a forward until the age of 12, when he switched to defence at the suggestion of his coach. With Ässät, he won the
Finnish U20 championship in the 2023–24 season. In April 2024, Boelius signed a three-year
Liiga contract to Ässät's senior club. He earned his first career Liiga point, an
assist, against
SaiPa on 12 October. Entering the
2025 NHL entry draft, Boelius is projected to be one of the top Finnish draft picks. He was ranked tenth among European skaters in
NHL Central Scouting's January ranking. == Career statistics ==