Kersten took part in the 2015 European Athletics Junior Championships in the 10,000 m, winning the bronze medal. In 2016, he became Belgian indoor champion in the 3000 m for the first time. In cross-country running, Kersten finished eighth in 2015 at the European U20 Cross Country Championships. The following year, he finished tenth in the U23 and won silver in the country classification with the Belgian team.