To the OP
I would say fix things that could cause injury, Otherwise let him throw and make sure it is fun for him.
For the discussion on 9U kids throwing XX MPH
In my observations the kids throwing in the low 40s at 9U are in lower level leagues
On our travel team we routinely face kids throwing mid 50s at 9U
We carry 12 kids on the roster. 7 are pitchers. 6 of those started their 9U season
throwing over 50 MPH
We put them on the gun twice a year Once in the spring and once at end of season to track growth and strength
Going into our 10U season this year. 3 of our kids are currently at 57+. The other 4 are not far behind.
I am more interested in the mental aspect of pitching. We are failing to coach the mental aspect in lieu of jugs guns and balance points too often.