User blog comment:AdventureWriter28/Raimon GO 2nd Season/@comment-5193181-20111231135100/@comment-4703969-20120103150828

15 isn't high school ._.

It was also stated that he was in Ninth grade, his 3rd year of Junior High.

Like I said, he was only a high schooler at the graduation match (Episode 127, the 1 year time skip after the World Cup arc).