I'm over 6'2 and I have and have had guns with LOPs ranging from 13-3/4 to 15-1/2 - and all fit well - it depends on several factors including the shape of the grip, drop, cast, pitch, etc.
Have him try a few shots and if he's interested, getting a youth stock for your gun might be feasible. (Of course, so would getting him his own.......
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