Pieterse spent some time training at the Blue Bulls academy, before joining the
Nelspruit-based for the
2014 Under-19 Provincial Championship. He made seven appearances for the team in
Group B of the competition, scoring seven tries, the most by a Pumas player in the competition. He scored two tries in his first match, a 40–27 victory over and a hat-trick of tries in their Round Five match against in a 60–29 victory. Further tries against and followed as he helped the Pumas to finish in fourth spot on the log. The Pumas lost to the in Pieterse's home town of
Kempton Park in the final, but he received a personal accolade after the season by being voted the Pumas' Under-19 player of the Year. At the start of 2015, Pieterse played amateur club rugby, making four appearances for the Witbank Ferros during the
Community Cup competition. The team failed to qualify from
Pool D, winning just one of their four matches. He rejoined the Pumas in the second half of the year, starting five matches for the side during the
Under-21 Provincial Championship. He weighed in with two tries – in victories over and – to help the Pumas win all seven of their matches in the regular season to top the log. The team did not take part in the title play-offs, however, since they were deducted all their log points after fielding ineligible players during the competition. ==2016: Western Force / Cottesloe==