2009-10: Ikonen skated for SapKo's U20 and U18 teams in his hometown of Savolinna and put up 33 points in eight games with SaPKo's U16 (C Juniors) team. Ikonen played in 14 games for SaPKo U20, which finished last in its region, and scored 13 goals with 8 assists and 8 penalty minutes. In four games of relegation play, he scored 3 goals with 4 penalty minutes. In five games with SaPKo U18 he scored 6 goals with 4 assists and had 12 penalty minutes. The fifteen-year-old was dominant against players his own age at the second division level, scoring 20 goals with 13 assists for SaPKo U16.
2010-11: Ikonen moved up to the top level of Finnish junior hockey, playing for KalPa in Kuopio, and skated for Finland at the 2011 U17 World Hockey Challenge. In 26 games with KalPa's U20 squad he scored 7 goals with 10 assists and was an even plus/minus on a team that finished 14th out of 15 teams. In the relegation playoffs, Ikonen scored 2 goals with 3 assists and was plus-five as KalPa successfully retained its spot in the top league. He played 10 games with KalPa U18 (including four playoff games) and scored 6 goals with 7 assists and 16 penalty minutes. In four games for Finland at the WHC he scored 1 goal with 3 assists and had 2 penalty minutes.
2011-12: Ikonen made his SM-Liiga debut for KalPa, was the KalPa U20 team's second leading scorer and represented Finland in the 2012 U18 World Junior Championship. In eight SM-Liiga games he had 1 assist and was minus-one with 4 penalty minutes; averaging nine minutes of ice time. In 37 games for KalPa's U20 team, he scored 17 goals with 28 assists and was plus-12 with 18 penalty minutes. In nine playoff games he scored 8 goals with 6 assists and was plus-five with 2 penalty minutes. KalPa reached the U20 bronze medal game. Ikonen played six games with KalPa's U18 team during the qualifying phase of the season and scored 6 goals with 9 assists. In seven games for fourth-place Finland at the U18 WJC he scored 2 goals and was plus-three with 4 penalty minutes. Ikonen was ranked 22nd amongst European skaters in Central Scouting's final rankings prior to the 2012 NHL Draft but was passed over in this draft.