I think what @intparent wrote is comprehensive and sane. He will need stem experiences (math-sci) and “real kid” rounding and other interactions with peers. Tinkering is a good trait, but he should engage in collaborative activities, not exclusively loner.
I do agree you can find much of your running start from stem-savvy posters here. I’m not sure how a parent, if not familiar with stem fields and opportunities, would even begin to vet a counselor (specifically for stem) who knows his or her stuff.
See how much his school offers, as a start.