I like to reference this as far as pitching velocity.
Could he be throwing maybe mid-80’s to high 80’s or even 90 by senior year if he puts the time and work in?
To answer your question, yes, I think if your son is dedicated and puts in the work, he can definitely increase his velocity. There is plenty of things online (and on this site) about things to do to increase your velocity. Perosnally, I use a program called TuffCuff by Steven Ellis and I defiently recommend the program.