Aho was 21 when the New York Islanders selected him in the fifth round (No. 139) of the 2017 NHL Draft. The 5-foot-10, 170-pound defenseman played three full seasons with Skelleftea of the Swedish Hockey League but was not drafted in 2014, 2015 or 2016.
The Islanders assigned Aho to Bridgeport of the American Hockey League, where he became the first defenseman in team history to score three goals in a game against Providence on Nov. 5, 2017. Aho had 20 points in 29 games with Bridgeport when he was called up by the Islanders and made his NHL debut on Dec. 31, 2017, against the Colorado Avalanche.