One of the reasons I started this was that I thought we had something to share regarding raising up a pitcher, so thanks for the questions.
"When your son was younger...about 14-15, what was in his arsenal?"
At 14-15 he was throwing a 2 and a 4 seam and a tight curve and a slow curve and started throwing the slider.
My son started throwing curves at 12. Now before I go and start a curveball war here, I'll add that he only threw in league, districts and the state champuionship that year, total of maybe 20 games all season, no travel ball at all until this prospects team he's on now. Instead we attended summer camps put on by UNF for a month each year until he was 16....I think he had a whole lot more fun with baseball and learned conditioning and fundementals from college coaches and players (He learned his slider from Bob Shepherd pitching coach for UNF for example....and also developed a world class pick off move or moves...they teach 5 or 6) while getting used to being around people who play at the higher levels.
"How has his elbow health been?"
The worst he ever had it, on his elbow, was a little bit of a tired arm in the transition from freshman to soph. He was over-worked by an inexperienced J.V. coach in summer ball when the guy just fell in love with his slider (In a district championship that year he struck out 14 of 15 faced, within another week he struck out another 13). He did have a labrium injury as an 8th grader going to 9th...summer ball again and that time he was on side by side mounds for the first time in an unfamiliar bullpen, while warming up the catcher on the side next to him threw right as he released and it made him flinch and fall off balance, the doctor (Dan McDonald Shands Gainsville) diagnosed a "crease" in his labrium and gave him pt and rest. He's been fine since
"did he throw a ton when he was 15?"
We have always thrown a ton as far as us playing catch, nearly every day for as long as I can remember (He got the bug as a little one watching me and his brother throw...he said he liked to hear it sizzle). As far as game throwing, well he throws a lot of cg's, but as I said we keep it, or kept it league ball, school ball, summer school ball...the soph to jr season he had around 10 cg's for the year
"very slight ache in the elbow during a bullpen session last week"
How is he now? If it went away it could just be conditioning soreness, keep an eye on it and make sure he can tell you about his pain (Acute or chronic or sore or etc.).
"about 10 pitches or so after throwing about 60 fastballs. "
Did you watch the pen? Was he laboring? Tired? Hard to tell but normally this isn't something or an amount I would suspect as a causal factor for injury, unless he just throws it wrong that is.
"Also how does your son hold the change...grip wise? Are there any secrets that he's picked up relative to the change while he's been there. i.e. pronating a little, etc."
Kind of a combination of circle and vulcan, his thing is to hold it loosely, backed up to his joint where the fingers join the palm and he does pronate and not pronate depending on how he wants it to act. It is the last pitch he's mastered and it's taken a little practice and use to get confidence. In the previous post you'll note he k'd 8 of 9 in the last 3 innings, well it was his change just making these guys look real bad (Half swings, give up swings..it was great to watch) he went to a sequence change and off his fb they just couldn't hold back (Throw his fb in an unhittable spot and then come back with the change starting down the middle then dropping off the earth).
Hope this adds to some of the things you think about when training Joe jr.