I wouldn't change this kid's arm-slot. What's the point of doing something like that? (I can give you a long, detailed rationale for not changing his arm-slot, if you are interested to hear it).
For a 9 yo he looks very good. On some deliveries he seems to lack balance after his stride foot lands, but jeez, what 9 yo can be expected to show a perfectly consistent and coordinated pitching motion on every delivery? Consistent, repeatable mechanics are obviously a goal for all pitchers, but certainly not anything to be concerned about in this 9 yo.
Personally, if I were this boy's dad I'd be much more interested in thinking about strategies for letting the kid have fun pitching at his current level while at the same time carefully monitoring his use.
ASMI has published a number of studies that conclude very persuasively that overuse is the major causitive factor for injury among youth pitchers. More surprisingly, if any one type of pitch is correlated with arm/shoulder injury to youth pitchers, it is the fastball. Shocking, huh?
Not really, because FB is the primary pitch for most pitchers, especially at young ages. The better, faster FB a young kid has, the more he's going to be used, because he will mow down the competition without fail.
The more he gets used at 9 yo - 16 yo, the more likely it is that the open growth plates in his arm can be affected. The temptation with a kid like this 9 yo is to show him off and "develop" him year-round with as much baseball as possible. And, these days, way too much organized baseball is accessible. Kids that spend all their time pitching and playing in organized games will generally not have enough time off for rest, low-impact mechanics work, off-season conditioning, and other sports.
I favor moderate pitch counts and plenty of days rest between outings at youth levels--especially if your 9 yo stud wants to have some glory years left in his arm by the time he gets to high school.
Sorry for the rant--take what you like from it, or disregard it if you've already thought this stuff through.