my brother is 14yo and tops out at 66,but does not throw strikes with consistency. any drills or mechanical tweaks.
I think it’d be hard to give any advice without video.
If a pitcher has a good arm but is having problems locating his pitches, it’s most likely a mechanical problem; it’s very difficult to control the ball if you can’t control your body and get to a consistent release point.
Post some video and we’d be happy to help provide feedback.