In the spare bedroom of a small brick house in East Point, Atlanta, the 22-year-old rapper Young Thug is crouched in a cramped, wooden closet, ad-libbing into a microphone strung from the wall.

I'm over 30. I was always part of the cool group in high school - always invited to parties (drinks, drugs) - that kind of person. Decent fighter (we all lose at some point), known as one of the ...