[5] In 2013, Kirsten was selected in the South Africa Under-20 team that attempted to retain the IRB Junior World Championship title that they won in 2012.

[13] In 2014, Kirsten represented Pretoria-based university side UP Tuks in the 2014 Varsity Cup, which ended in disappointment as they finished in sixth spot to miss out on the semi-finals.

Having previously played as a lock, Kirsten started their match against UCT Ikey Tigers as a flanker[14] and remained in this position for the Blue Bulls U21s in the 2014 Under-21 Provincial Championship.

[15] The Blue Bulls reached the final of the competition and Kirsten finished on the winning team, as they ran out 20–10 winners over Western Province U21.

[16] Kirsten started seven of UP Tuks's matches in the 2015 Varsity Cup, contributing tries in convincing victories over Maties[17] and CUT Ixias[18] as they topped the log after the round-robin stage to qualify for the semi-finals.