Much good advice in this thread. It’s been a while since my son was in high school (when I joined this forum), but a few things I would say in looking back that helped him on his path to becoming a professional musician:
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Make music for the joy of it. Music should never be a chore. Let him practice and play because he wants to, not because anyone is forcing him to.
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Subject to (1), play as much as he can. Sessions with friends, jams, school groups, extracurricular groups. Even paid gigs if they present themselves. Never too young to be putting yourself out there.
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Listen to music. My son had probably a thousand albums on his computer hard drive, including multiple versions of all the standards. He listened and learned. Also went to as much live music as he could. (It helped that he was in NYC, where there are amazing musicians playing at many venues every day, but you can find live music wherever you are.)
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Develop repertoire. As a jazz musician, the more music you know, the better.
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Summer programs. My son’s first was at Eastman, where he realized, being surrounded by students as passionate about the music as he was, that this is what he was meant to do. He also did summer programs at Stanford Jazz and Skidmore. But there are many great summer programs.
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Find older mentors. Mentoring is a tradition in jazz and there are older jazz musicians who are open to taking the young ones under wing.
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Not sure whether this is more unique to my son, but even after he made the decision to focus on jazz, he continued to play classical music and take classical lessons. Even in college / music school and even after graduating and becoming a full time jazz musician. He feels it helps him both with technique and with musical ideas.
As a rising 9th grader, your son still has a lot of developing and exploring ahead of him. Let him find his own path and decide what excites him and what motivates him. From fairly early on, my wife and I took the approach of being there to encourage and support, but otherwise just to stay out of his way. Also, all of the foregoing are ideas and suggestions, not a checklist. Again, let him find his own path.