From what I've read, he wants to spend more time with his family, especially with his kids being interested in starting their own racing careers. Not to mention, he is the oldest currently active driver at age 47, so the question of his retirement has been asked quite a bit in recent years.
6
This is my favorite number of all for a lot of reasons. I could write about many of those reasons, but I'm sure by the time I finish it, someone will have already posted that number in this topic, so I'll save that story for another time.