All of which makes perfect sense to Bill Wax of XM Satellite Radio. "To do the blues well, you need a certain amount of experience in life. That's what the blues are about - songs about life, so it requires some maturation," says Wax. He acknowledges the talent of young blues artists like Johnny Lang, Shemekia Copeland, and Monster Mike Welch, all under 25, but adds a word of caution: "Periodically, the media jumps on some 17-year-old guitar player and makes him into the next big thing, and then the kid gets interested in some other kind of music and we never hear from him again."

Peter Guralnick, on the other hand, disputes the notion that the blues is a graybeard's art, noting that ur-bluesman Robert Johnson died at 26 or 27 (poisoned, the story goes, by a jealous husband), and that Elvis and Sam Cooke were "fully formed and making extraordinary music" by the time they were 21. "I wouldn't set up any hard and fast rules [about age]," says Guralnick. "Some people take longer to mature than others, but how old was Hemingway when The Sun Also Rises came out?" (He was 27.)

It's too soon to say he's the "future" of the blues, but the career of Chris Thomas King, 38, certainly testifies to the challenges of blending the blues tradition with contemporary influences. With 10 albums under his belt and his own record label, 21st Century Blues, King gained a wider following after playing Delta bluesman Tommy Johnson in the Coen brothers' 2001 hit movie, O Brother Where Art Thou? The O Brother soundtrack, carrying King's version of "Hard Time Killing Floor Blues," sold more than seven million copies and earned a slew of Grammys.

For the PBS blues series, King plays Blind Willie Johnson, another seminal blues figure, in Wim Wenders' film "The Soul of a Man." It's ironic that King should be identified with the blues' sepia-tinted past, because his own music stretches and bends the blues to the breaking point.