http://www.youtube.com/watch?v=xjV2HKpugTM
Take a look at Cole Hamels. One thing that might help with the hip/shoulder separation (delaying shoulder rotation) is to keep the glove out front like Hamels and most major league pitchers do. Your son's glove appears to swing towards his right hip which can cause the front shoulder to open early. Keep the glove out front and let the glove and chest meet.
Best advice I can give you: find a good pitching coach and develop that lefty.