I write lefty, and I shoot right handed, I am "mixed dominant" meaning I have no truely dominant eye, My strongarm is my right arm, I play baseball right handed, football, but I shoot pistols ambidextrious, I guess I'm wierd..
Although when suggested I refuse to shoot longguns lefty, I get advise like I've never picked up a guns on occasion, and Just say thanks respectfully enough and Break a 23/25 on clays, or shoot a 2.25"x2.5" group at 300 yards..
and I'm 14, been shooting like I have since age 7, and I wouldn't mess with your sons way of aiming, his body knows best, and that will always be the case in my opinion, because of how I personally shoot, and do other things.
It's nearly impossible to change a dominant eye, though my left eye is dominant more days a week than my right eye is.