In 2013, Steenkamp was named captain of the South Africa Under-20 squad for the 2013 IRB Junior World Championship. He started all five matches for a South African side that won the competition in 2012 and attempted to retain the title in the 2013 event held in France. They started off in fine fashion, beating the United States 97–0 in the opening match. Steenkamp scored a try midway through the first half as South Africa ran in 16 tries. South Africa secured a 31–24 victory over England and a 26–19 victory over the hosts France to finish top of Pool A and qualify for the semi-finals. However, a 17–18 defeat by Wales eliminated the defending champions from the competition. They recovered in the third-place play-off match to beat New Zealand 41–34, with Steenkamp getting his second try of the tournament shortly after half-time.