Keith recently told ABC News Radio that it was SCHOOL that he quit at age 15! 

"I was hopeless at school.  I was out.  I would've left sooner if I could, but you've gotta legally stay 'til you're 15."  But he added, "Look, I'm always very careful to not have parents think I support leaving school at a young age, 'cause I don't necessarily.  All I can speak is my own experience is that I--the biggest education that I got was when I hit the road and got life's education.  That was everything that school didn't have to teach me at the time." 

Country Weekly