When I was 15 my Dad gave me one of his old work trucks for my birthday. It had 300k on the clock and needed a new engine. He bought me a used I-6 300ci and helped me swap it out. One of the best father son times I had. This kick started my passion with anything with an engine. Now I have had a few cars I have restored/raced/crashed/and restored again.
So when it came time for my kid to start driving I did the same thing. I bought him an old dodge with a 360 that was toast for his 15th B day. And a junk yard 5.9 to replace it with. We swapped out the cam/lifters, added some new bearings, swapped it out from fuel injection to carb. Added a set of heads/headers. He learned a fair bit, and it was so cool to see him pull it out of the garage and drive it down the road. He had a few hickups, that inch ponds vs foot pounds got him a few times, snapped off a few bolts!
He has sold that truck and now is onto car number 5 at 17 years old. Rebuilding a vw gti engine in one, and now onto BMW's. I believe his mechanical ability's has surpassed mine at this point. I stick to stuff 1980 and older, he is strictly 2000 and newer. I refused to work on the BMW's as they need so many special tools that I just don't have. So its all him now days. I still help him out when I can, we just installed a header in his 330ci. It should have been a bolt in deal. 2 days later and about 10 hours of cutting/welding it fit like a glove, happy I can still teach a few things to him.
Young mechanics are harder to find now days, but they are still around and upcoming.