He appeared on two occasions in 2012 – now mainly playing as a loose forward – as Eastern Province U19 reached the final of the competition where they lost to near neighbours Border U19.
He represented Griquas U19 in the 2013 Under-19 Provincial Championship making four starts as a loose forward and scoring tries in consecutive matches against Griffons U19[2] and Limpopo Blue Bulls.
Koza was also named in their squad for the 2014 Currie Cup qualification tournament and made his debut in that competition in their 52–5 victory against the Border Bulldogs.
Koza made two starts and one appearance off the bench during the 2015 Vodacom Cup competition, helping them finish in second position on the Northern Section log, before they lost in the semi-finals to the Pumas.
[8] In the second half of 2015, he was once again mainly used by the Griquas U21 side, starting seven matches for them in the 2015 Under-21 Provincial Championship Group B, as they reached the semi-finals before losing to Limpopo Blue Bulls U21.