There are some great studies done by the College of Orthepedics on "Little League Elbow". This is specifically an overuse injury to the medial growth plate of the elbow complex. This plate "usually" begins to harden between 14 - 16 years of age. An estimated 40% of youth pitchers will experience some growth plate issues according to one study! Most are generally mild and only require rest. Scaring, fracturing and detachment and the rare but potential risks. Even these are treatable by surgery with great prognosis though. My concern is that at his age, maybe it is not a growth plate issue at all. I would be concerned about the ulnar collateral ligament which presents with almost the same symptoms.