Per this interview (http://www.youtube.com/watch?feature=player_detailpage&v=nld8B9l1aRE), he took CS classes in high school and had some mentoring from his uncle early on.

My friend also met with him recently and asked how he learned out of interest and asked if he took programming courses at Stanford, which Kevin said yes, but his interview in the video above doesn't line up with that response (albeit I heard this second hand so I can't verify the convo).

So what is the truth?