The guitarist and singer Buddy Guy has been playing since he was a boy, and learned from such masters as Muddy Waters and Howlin’ Wolf. But at age 87, the recipient of eight Grammy Awards is not slowing down; in fact, what he’s calling his worldwide “Damn Right Farewell Tour” is scheduled to run until at least next May, and maybe beyond. Correspondent Kelefa Sanneh talks with Guy about his blues journey. He also sits down with three of Guy’s children to discuss the musicianship they’ve inherited.