Metallica’s members are all in their 60s, and their music is way more physically demanding than anything their classic-rock forebears have had to tackle onstage — but lead guitarist Kirk Hammett tells our Rolling Stone Music Now podcast that he doesn’t see retirement on the horizon.

“As long as we have our health and our mind, I think we can just keep on going,” says Hammett, whose new coffee-table book, The Collection: Kirk Hammett, dives into his world-class arsenal of vintage guitars. “Sometimes I forget how old I am,...