At that age he will probably want to see results rather quickly.
Showing a C program that can do array manipulation probably isn't going to do it for him.
While C++ and Java are
the languages to know at this moment, I think Java has the most likeability to someone his age. Perhaps looking for a few good Java tutorials that show quick results (anything moving will probably suffice) will do the trick. Once he has a starting point, he will very quickly decide what he wants his 'example' to do next and start to adjust it to his liking.
Googling I found this link from an originally swedish tutorial:
http://www.mandomartis.com/onlinecou...roduction.html It looks promising. And remember while most games he plays will be probably be written in C (or derivative) learning Java will help him considerably when learning any new Object Oriented (OO) language like C++ in the future.