Call me old school, but I would start off with Basic. If he was younger I would recommend Logo. Once he's hooked I would get him into C or pascal. I can't recommend enough getting him a "Basic Stamp" kit. Seeing how software can control hardware is magical. Then work him up into "Arduino" world in C.
BASIC will scar him. You might as well go with ruby or python, you get the same facility and start off with an extensible paradigm.
Didn't we all start with basic, even if just for a little bit?