Maybe the post should have asked when will lifting be beneficial for baseball? In my opinion the answer to that is when he has hair under his arms and some fuzz on his face that needs to be shaved about once a month. Then he will have enough testosterone in his system to change his body from lifting. Prior to that time he's more at risk to hurt himself, although that is always a concern with improper supervision and technique. Age 11-13 is where I saw the most injuries, and I don't think that it is a coincidence that that is when the body is changing the most. So, my advice is to take it easy during the big changes and start the lifting when the huge changes are done. Not all changes, just the huge changes.