I would stick with the .22L for awhile. Scavenge around through your local shops and gun shows to find a real .22L target rifle. There are always some used inexpensive single shot bolts with match barrels and nice triggers to be had. Then mount some less-expensive <$150 glass on it and you are set. He will be able to shoot that comfortably, and cheaply. Practice, practice, practice. My .22L Anshutz will hit sub MOA at 100yrd with match ammo believe it or not. All I did was clean the bore when I got it, and mount an $80 BEC scope on it. The single shot bolt forces a little more discipline to not waste shots and concentrate on each one. He could iron out a lot his shooting habits with it. Then it is still a fun gun to have, and you can break in new shooters with it – he will enjoy doing that later.
One day when you think he is ready and can afford it, get him a quality .308 with a 26” barrel. He could then start learning more with the “real thing” and getting used to its bullet drop/recoil and concentrate on more specifics since most of the other aspects of shooting at a range are very familiar to him. Then he will shoot more expensive ammo also, so get your "training mileage" out of the .22Ls first. If in his early youth you want to jump right into getting him a real rifle cartridge, I suggest you get him a shooting jacket as well.
I think most importantly you should get him involved with skilled individuals. The years of knowledge and skills developed in him would have far more benefit then any rifle you buy him. You don't want to cultivate bad shooting habits, he needs some coaching. Small bore competitions at your local gun clubs is a good way to start. Get them to teach him best how to shoot standing/kneeling/prone and to zero scope/sights off the bench. You can set up his training exercises to mimic the service's high power qualification programs. That way it will be an old familiar test for him when he takes it.
Make him take decent math and physics in school, get him into scouting, make sure he likes to go camping and spend time in the brush.