[2] At primary school level, Mahlo earned provincial colours in hockey and cricket, as well as representing the Limpopo Blue Bulls in the 2006 Under-13 Craven Week rugby union competition.
Mahlo again represented Limpopo at the Under-16 Grant Khomo Week competition in 2009 – which also earned him an inclusion in the Under-16 South African Elite squad – and played at South Africa's premier high school rugby competition, the Craven Week on two occasions; he played at fullback in the 2010 edition held in Welkom, scoring a try in their match against the SWD Eagles[3] and also in the 2011 edition in Kimberley, where he started all three of their matches in the scrum-half position.
At the end of the season, Mahlo was invited to join a South African Under-20 training camp in preparation for the 2013 IRB Junior World Championship in France, but missed out on final selection.
[19] Mahlo made his first class debut for the Blue Bulls during the 2014 Vodacom Cup competition, coming on as a second-half replacement in their match against the Griffons in Welkom and helping the side to a 49–0 victory.
[25] Mahlo made a total of three starts and six appearances off the bench in the Blue Bulls' 2015 Vodacom Cup campaign, helping them all the way to the semi-final of the competition, where they lost 6–10 to Western Province.