Re: S KITS?
What I would do would be to order templates for the body, and get a neck from a licensed neck/body maker, like Musikraft, Warmoth, USACG, etc. (Or get a used Fender neck off of something good like a MIM Classic Series, MIJ Fender, MIA Fender, etc.) Without building the body yourself, you really aren't doing much more than putting a bunch of parts together. It's fun for a bit, but only minimally educational. Building the body from raw materials will teach him good, basic, and fun woodworking things, like wood selection, jointing, gluing/clamping, planing, routing, and sanding (not to mention finishing). Building a neck is a bit more advanced. It is not the hardest thing in the world to do, if you are set up for it. However, it might be a bit beyond the level of "building" you want to do with him, at least for now. The radiusing, fretwork, and nut work in particular are better suited for a second or third build IMO.
For that look, you probably want to scavenge some old, weathered wood, or take the body you've already made to a sandblasting company. Have them minimally blast the wood, just to sink the areas in between the grain a tiny bit. Then stain, then carefully sand down the high spots to lighten them. You can do this in multiple stages with various colors of stain for a more natural look.