My son is also a 2020, and has had back issues, though he has a specific back condition(Scheuermanns Variant). Now, that's not the same, but wanted to relay the info. He also had a bit of a growth spurt last year, he just went past 6' and not rail thin but strong/lean at around 155 lbs, growing 2" this past year, but more like 4-5" the year before, when the problems began. I know there are some 6' 180lb man childs out there at 14, but not him.
We did go to an Ortho and ended up going to PT, and have followed that up with him working with a personal trainer. The focus, per the Ortho and PT, was core strengthening to support his back. He goes 2x a week usually, and they do a lot of core work, but do hit legs as well and introduced some lifting. Core work is the focus, to support his back, and is good for him anyway. In addition, his baseball training 2-3x a week, has about 1 to 1-1/2 hours of training, but that's more of your dynamic/agility style exercises. Overall, it has been great, especially working with the personal trainer.
He's not the most athletic kid, partially I think due to not having the strength to handle his height, but the past 6 months has brought some noticeable improvement. He's improved in many areas, speed, big increases in things like box jumps, etc.
The most important thing is that, other than a minor soreness for one day, he has had no back pain in the past year, or anything he's told us. If he ignores this, it could result in kyphosis later on, which is my concern, far more than anything baseball/sports related. Knock on Wood big time that it continues well.
A visit to the Ortho or at the least a PT for an injury screen(often free) may be worthwhile, just to rule something out and/or catch it early. In any event, my son has benefited very much from the strength work.
Best of luck to your son on getting this behind him and the upcoming season!