As other folks have said, it's helpful to understand very roughly what sort of thing interests him. For example, making iPhone apps, making OS X apps, web design, etc and focus on something that's going to guide him in that direction. I started out on AppleScript with a little Javascript thrown in many years ago but I wouldn't recommend either of those as being sensible entry points.
I'm no fan of Python, but many folks seem to think its a good starting point. Personally, I'd look at some form of C or maybe Swift. Depending on the age of the kid, there are plenty of resources nowadays aimed at getting kids into coding, for example
https://www.tynker.com (disclaimer: I have never used that site, it's just an example!)
Good luck!