Well see, we aren't that far apart.
11-13 is when I saw the most injuries. 3 catchers having surgery, 2 hips just tearing away from the bone, and 2 kids in a full arm up to shoulder cast because they screwed up their growth plate. At least 5 of those kids had been doing stregth training since third grade, the other two I didn't know that well. I also saw a 12 year old blow out his arm on the mound at Lakepoint, he was from TX and was pitching 75, didn't know him either, but injuries at that age were just life altering and very scary.
I was fortunate in that my son was an early bloomer, he was shaving at 13, but in my opinion he was better served by speed and agility teaching him to learn his new body than lifting weights. He grew 12 inches in 13 months, he was 6'2 at age 14. Every part of his body was already stretching so quickly I was worried about any additional stress, plus he's also "that kid" who sees Bubba squatting 300#'s and wants to give it a try.
Overall I have no regrets. For anyone not shaving yet, my very unqualified opinion, is to do speed and agility rather than strength training. Speed and agility allowed my son to learn how to move his body so that when he all of a sudden had tall lean legs he knew how to use them (love zztop)! I'll admit for awhile he looked like a newborn giraffe, and he banged into more than a few walls, but it all worked out. He is a very athletic kid who throws and hits faster than most so he's a happy guy.