Buy him or her a Raspberry Pi if they don't have a computer yet. Once on the Internet, any kid can find out the rest.
Programming in Python, then assembler (perhaps on a simulator?) is fun for some kids, and fosters an understanding of algorithmic principles and the operational precision required to make the machine do what you want.
There may be like-minded teenagers around? Learning together is more fun. A good model is having peers to learn with, and occasional access to mentors (watching people to program is faster than reading books). Some cities also have makers labs that anyone can use.
I think the internet is a great resource and a huge distraction. You can start looking for some "very specific thing" and 2 hours later you can't remember why you opened the browser.
The raspberry pi is a great suggestion, but I'd mix your suggestion with another on here: dump the kid at their grandparents house with a 286 and a BASIC book, and take their phone away.
Programming in Python, then assembler (perhaps on a simulator?) is fun for some kids, and fosters an understanding of algorithmic principles and the operational precision required to make the machine do what you want.
There may be like-minded teenagers around? Learning together is more fun. A good model is having peers to learn with, and occasional access to mentors (watching people to program is faster than reading books). Some cities also have makers labs that anyone can use.