Välimäki was named to team Finland in the 2017 World Junior Ice Hockey Championships, scoring two goals in six games as Finland finished with only one win in the tournament. In December 2017, Välimäki was named captain of Team Finland at the 2018 World Junior Ice Hockey Championships. Finland was subsequently eliminated in the quarterfinals against the Czech Republic with a final score of 4–1, and Välimäki finished the 2018 World Juniors with one goal and three assists in six games.