Personally I think you can get him up on that board. I have a cheap beginner board that is actually very large at 5'4" so it helps them go wireless quickly and it sinks easily for beginners to angle over with a touch of heal pressure making it easier to get up out of the water.
My son is 8 and is now surfing on my NSP Fish 60 which I would guess has 50% more volume than your board making it tougher for kids to get up on.
For tips: with the boat just above idle my son can pull himself out of the water on the board, then I accelerate to surf speed.
When pulling them up, turn to the surf side so the surfer is not in the prop wash when the are getting up and don't have to drop in on the wave when they get up. You can hook the tow rope to the surf side of the tower instead of the center.

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