Stop; don't do it. Your love of programming doesn't automatically make you a good teacher and layering inexperience on the ingrained patterns of behaviour between brothers will be a problem. Next assess if you want him to learn or if he wants to learn. If it's the first, consider that strike three.

Now, assuming he actually wants to learn and approached you for advice, start him with something fun like Bootstrap, http://www.bootstrapworld.org/, based on Scheme, or Scratch, http://scratch.mit.edu/Smalltalk, based on Smalltalk. He'll learn fundamentals in a well-designed language and have a community of educators and students to interact with.

The point is that it's not an operating system or a text editor. It is, paraphrasing Alan Kay, a construction material, designed for building things that work with text.