De Klerk grew up in Pietersburg (now Polokwane) and was selected to represent Limpopo at the Under-16 Grant Khomo Week in 2007.
After high school, De Klerk moved to the Western Cape and was linked up with Cape Town-based side Western Province. He made nine appearances for the Western Province U21 side during the 2012 Under-21 Provincial Championship, helping the side to third spot on the log to qualify for the semi-finals. He started their 19–18 victory over the Sharks U21s in the semi-final, as well as in the final, where he could not prevent his side suffering a 13–22 defeat to the Blue Bulls U21 in Durban.
He was included in the Maties squad for the 2013 Varsity Cup competition. He helped them to finish top of the log and beat the NMMU Madibaz 16–15 in the semi-final, but once again lost in a final, this time 5–44 to UP Tuks.
He returned to Varsity Cup action in 2014, starting all eight of their matches during the season and scoring a try in each of their matches against Johannesburg-based rivals – one in an 18–15 win over Wits and one in a 24–8 win over UJ. Maties finished third in the competition to qualify for the semi-finals, but were unable to beat their Cape Town rivals UCT Ikey Tigers, losing the match 8–20.