Välimäki was named to team Finland at the 2015 IIHF World U18 Championships, which eventually earned a silver medal after a 2–1 overtime loss against the United States. Välimäki finished the 2015 tournament with 1 assist in 7 games. The following year Välimäki was named captain and led Finland to the gold medal at 2016 IIHF World U18 Championships defeating Sweden 6–1. Välimäki finished the 2016 World Championship with two assists in six games.