IMHO the most important thing is to keep his interest continuously for several years. I would suggest these steps:
1: Finding what is interesting for him - games, web, automation, hardware, etc. Open source project or good step-by-step tutorial is good starting point.
2: Preparing a build environment
3: Building and running
4: Doing small change in the sources - renaming something, etc.
5: Building and running again
...
N: messing deeper with the source, changing complex things
N+1: Building and running
In that way he will learn the fundamental process of building something in small steps and endless iterations, messing with other peoples code and navigating easy in it - that one is important too.
Comments
IMHO the most important thing is to keep his interest continuously for several years. I would suggest these steps: 1: Finding what is interesting for him - games, web, automation, hardware, etc. Open source project or good step-by-step tutorial is good starting point. 2: Preparing a build environment 3: Building and running 4: Doing small change in the sources - renaming something, etc. 5: Building and running again ... N: messing deeper with the source, changing complex things N+1: Building and running
In that way he will learn the fundamental process of building something in small steps and endless iterations, messing with other peoples code and navigating easy in it - that one is important too.