Skylark,
I went through this with my 2015 when he was 13. Now he's a catcher.
First, I heartily agree with you that there are too many factors involved in elbow and shoulder injuries to point to a single factor, or even multiple known factors. All the studies I've ever read say the same thing. There simply aren't enough comprehensive studies yet.
However, I don't think Josh's doctor told him that he "tore" the ucl at 9, he probably surmised that the ligament was gradually damaged over many years. The ucl is not likely to tear until the growth plate has fused to the bone. I know several young pitchers who have torn that plate loose. One had surgery to screw it back in place, the others let it heal on it's own.
Now as far as most college pitchers starting at a young age, I'll give you an intentionally outrageous analogy. All of the elderly smokers that I know started smoking at a young age, and they're still going strong. :-)
I've compiled some reading material over the years. Let us know if this is what you're looking for.
http://www.hopkinsortho.org/ucl.html"These stresses create microscopic tears in the ligament, which can add up to one big tear over time. (Figure 2) This gradual stress causes the ligament to stretch and become too long. Once it gets too long, it no longer holds the bones tightly enough during throwing activities."
http://ajs.sagepub.com/content/30/4/463.full.pdfEffect of Pitch Type, Pitch Count, and Pitching Mechanics on Risk of Elbow and Shoulder Pain in Youth Baseball Pitchers
http://www.abe.msstate.edu/Too...eball%20Pitchers.pdfPrevention of Arm Injury in Youth Baseball Pitchers
"In the age group 9 to 14 years, a high pitch count and also breaking pitches (curveball, slider) were significantly associated with an increased risk of elbow and shoulder pain. The study was statistically underpowered to show a significant risk of joint pain related to pitching mechanics. An increasing pitch count and cumulative count through the season was linearly associated with an increased risk of joint pain. It was therefore recommended that not only should pitch count be limited but season cumulative pitches as well."
http://www.littleleague.org/As...s/media/UNCStudy.pdfThe Learning Curve: Little League Seeks to Address Concerns, Answer Questions about Curveballs and Overuse
http://ajs.sagepub.com/content/33/11/1716.full.pdfBiomechanics of the Shoulder in Youth Baseball Pitchers
http://www.chw.org/display/PPF/DocID/41203/router.asp"LLE (Little League Elbow) may be used to describe a spectrum of disorders from a stress reaction to avulsion fractures of the medial epicondyle to osteochondritis dissecans of the capitellum and loose bodies. It occurs most often between 8 to 15 years of age."
"After physeal fusion, the ulnar collateral ligament and ulnar nerve are more likely to be injured."