Aspenes made his first biathlon appearances at the Junior European Championships in 2017 in Nové Město na Moravě.

Just a year later, the Norwegian won his first international title, unexpectedly triumphing in the pursuit race at the 2018 Junior World Championships.

Aspenes made his debut in the IBU Cup three years later in Obertilliach, immediately achieving a good result with 12th place in the sprint.

Before the turn of the year, he already had a podium finish and another top-10 result to his name, earning him a place alongside three other athletes as a replacement for the absent A-team in the Biathlon World Cup in Ruhpolding.

However, he ended the season by becoming the Norwegian champion in the sprint, comfortably distancing himself from Vetle Paulsen and Johannes Thingnes Bø.