From Santpoort-Zuid, Dobber made his international debut at the 2013 European Youth Olympic Festival, finishing seventh in the 200 metres and taking bronze in the 4 × 100 metres relay alongside Joris van Gool, Rutger Postma, and Sander Brugge. In 2014, he was a finalist at the Dutch under-18 championships in 2014 in 60 metres, 100 metres and 200 m, and repeated that feat at under-20 level the following year. Dobber won Dutch under-20 titles in 200 m indoor and 400 m outdoor disciplines in 2016. These results earned him selection for the 2016 IAAF World U20 Championships, where he reached the semi-finals.