I don't think any college trade school will accept him at his age. It's a matter of a minor possessing a firearm and I doubt if the (adult) instructor will accept responsibility for that. I can't speak for the AGI videos (we had them at TSJC, but they were stolen) but I know Bob Dunlap when he taught at Lassen College. You can learn so much from a video, but sometimes you need to consult with a person.
So for now, he should read. Walter Howe's Professional Gunsmithing is one of my favorites. Besides reading, he could learn some very important skills that are very relevant to firearms. This would include:
Machine operations (lathe, milling machine)
soldering
Welding (especially TIG welding)
brazing
Tool sharpening (chisels, gouges, drill bits, machine bits). Besides stones, he should have an introduction to grinders and especially grinder wheels (wear a mask and goggles).
Hand tools.
This may sound boring, but filing is an important skill too. Long forward stroke, lift up, pull back (but not on the workpiece). Holding the file right keeps you level too (you can have the thumb down on the file and not file handle).
All those skills were taught to us at TSJC gunsmithing. When he's 18, send him either to a school like TSJC or to its NRA summer school. That way he can figure out if he really is interested instead of going hog wild and spending a ton on tools and tuition only for him to wish he were a photographer or sports announcer.
Now, there are some good videos out there, and there is some trash. Here's an excellent monkey-see, monkey do video on the Beretta 92.
https://youtu.be/heKAnIMSwy4
Guns are held together by:
Pins
Screws
spring or mechanical tension (this includes solder/welding)
interlocking parts
He should also learn the basic principles of how a gun works. You need this to diagnose malfunctions.
BTW, I hate those Gun Digest books on assembly & disassembly. Their photos never show the critical (difficult) part and you have to figure it out on your own. Save your money.