You didn't say anything about the boy's interests. That's what matters most. A lot of young people (and older ones!) find tinkering arduinos to be a lot of fun, either making robot-type devices or making sensors to monitor the environment. Others like games, and would enjoy exploring that area. Still others might be interested in mathematics. And so on. Build on existing interests.
I wonder if there's a typo in your message. If the boy is 18yo, then an interest in programming will have already surfaced. Don't try forcing him to do something that's not of interest to him. You only have him at home for short while now. I'd encourage you to explore what he likes to do. Maybe you'll find a new interest, and the two of you will have a great time before he leaves home.
I wonder if there's a typo in your message. If the boy is 18yo, then an interest in programming will have already surfaced. Don't try forcing him to do something that's not of interest to him. You only have him at home for short while now. I'd encourage you to explore what he likes to do. Maybe you'll find a new interest, and the two of you will have a great time before he leaves home.