Koppers began his footballing career in Utrecht, playing for the local amateur side SCH'44 in the town of Harmelen as a striker, before getting recruited by Ajax to join their youth ranks. Under coach Sonny Silooy it was quickly noticed that Koppers strengths lied in defending, after which he was moved back to a more defensive position on the pitch. Currently serving as a left back for the Ajax A1 youth selection, Koppers appeared in his first match for the senior squad on 23 October 2011, in the 'Klassieker' derby against arch-rivals Feyenoord, starting in the left back position and playing the full ninety minutes in the 1–1 draw at home. On 31 January 2013 it was announced that Koppers would complete the 2012–13 season with ADO Den Haag on a six-month loan spell. While in The Hague, Koppers made 14 league appearances, helping his side to a 9th-place finish in the league table.