Son 6'1 and sitting 152lbs. As we turned the next chapter, here are my thoughts and experience; I have some engineering back ground and played sports in HS.
Pitched in his last summer/HS game with his teammates, in his last game which was the playoffs, he struck out 17 batters, 7ip, and 98 pitches thrown, 3 pitch kid (fastball, curve and change)cruising 88-90 the whole game, touched 91 and 92, the 98th pitch was clocked at 89mph with pocket radar. Was recruited mostly by D3s, an offer from D2 and few D1 interests, almost all local D3 wanted him to visit their facility, got a full ride to a JUCO, but he turned that down, sigh. On his collegiate team he pitched 27ip, 24k with 2.9 ERA.
At the end of the day, and maybe due to his lack of academic preparedness, he decided on a local D3 school.
Our journey was to get to 90mph, we were hoping that baseball would help him to get into a college, instead baseball got him into a college.
We did not use weighted balls, we lifted weights for 3 months in his junior year only thinking he stopped growing but once we found out his growth plate was still open, we stopped the lifting. When we did lift, we did squat as our heavy leg work out, mostly light free weights for the upper body and plyometric for developing the quick muscles, and all this could be found on youtube.
One main thing we focused on this journey was hip-shoulder separation throughout the years and even still. Every year except for one when he was relegated to the OF only, 12u and was run by daddy ball he gained 3+ mph on his velo. He pitched in a game once a week and threw more than 50+ pitches in all of his outings after 12u. If we knew he was to be idled for more than a week, we added a long toss session, for that week. There was a correlation between growth (height/weight) with increased in his velo and in his Junior year because of the weight lifting his velo increased by more than 5+mph. There was no magical workout, instructor that assist him to increase in his velo. At 13u, the topvelocity guy (Brent) came out to our area, spent $599 for the camp and all he said to me was, keep doing what he is doing, biggest waste of my money!
In ten years our son never complained about his arm, in 98% of games we made sure that he wasn't being abused, only 3 games we recall, when we knew it was the last time he will be pitching for the season did we allow him to throw more.
On this forum, there has been a wealth of experience, knowledge and common sense. Thank you.