[2] Riethmüller's first international competition was at the 2016 Winter Youth Olympics in Lillehammer.

He finished in the top 10 three times in the individual competitions and won with team Germany a silver medal in the mixed relay.

[3] In 2017 he took part in the youth category at the Biathlon Junior World Championships in Brezno-Osrblie, where he achieved 3rd place in pursuit, individual and in the relay.

[4] In 2019, Riethmüller took part again in the Biathlon Junior World Championships, which, like in 2017, took place in Brezno-Osrblie.

He was able to land on the podium in his debut season with a 3rd place in the sprint in Martell.