He went to Hoërskool Klerksdorp and was selected to represent the Leopards at the Under-16 Grant Khomo Week in 2010,[2] scoring tries in their matches against Griquas[3] and Border Country Districts.
[4] In 2011, Koen was named in the Leopards team that competed at the foremost rugby union competition at high school level in South Africa, the Under-18 Craven Week.
Koen also started the semi-final against Blue Bulls U21, but the team from Pretoria won 37–21 to end the Leopards' interest in the competition.
He made eleven appearances for the Kimberley-based side during the 2016 Currie Cup qualification, scoring his first senior try in their 36–14 victory over a Sharks XV,[20] as Griquas won eleven of their fourteen matches to finish the competition in second place[21] to earn a spot in the Premier Division of the Currie Cup.
He made his debut in the Currie Cup's Premier Division as a replacement in their first match of the season – against former side the Sharks[22] – before making his first start a week later in a 30–24 victory over defending champions the Golden Lions.