Most will tell you to get a 6'6" soft fish for him, but I see nothing wrong staying on the 8'0" to build up muscle memory and learn to use the rail.
SilentFox18 wrote: He is able to catch white water and ride it into the beach.
Thus he is going straight. You need to be able to trim across the open face of the wave and then engage or disengage the rail to fall up or down the face. Tip tapping and wiggling the nose back and forth in the white water soup is not turning. You can veer and angle but not really turn because you're riding on the flat bottom of the board.
My advice is to WAIT until he can paddle in to green waves. Angle in ( or you can push him in at an angle ) and go from peak to shoulder consistently. Then he can start to do turn downs and later turn ups. That will build up a strong base that will help him later on as he moves down to smaller boards.
Johnny the ripper was not that heavy and riding a 9'0". Notice how he gets onto the open face and steps back to the tail to turn when it's time to cutback ( comeback ) to the curl.