Robert Plant, 73, is often asked about retirement. After many decades in the industry, both fans and journalists alike have wondered — and questioned Plant directly — about his retirement status. But the former Led Zeppelin singer can't even fathom it.

“People used to say to me, ‘Well, you must have done enough now?’" Plant said in a new interview with the Telegraph. "Enough of fucking what? ‘Enough to retire!’ So imagine the blessing to be 40 years further down the road, and I still don’t know enough to stop in any respect. There’s always something new to learn, somewhere new to take it. I love it.”

As Plant put it, working as a musician is a "lifetime's job," one that continues to fulfill him in older age just as it did when he first became interested in rock music. Plant, notably, has released more solo albums than any other former Led Zeppelin member and is now scheduled to go on tour next year with bluegrass star Alison Krauss, with whom he just released a second album, Raise the Roof.

Similar to the duo's first collaborative LP, 2007's Raising Sand, the new collection of songs has offered Plant, well known for his powerful lead vocals, the chance to work in an entirely different fashion. "It’s like being at night school,” he said. “I’m still learning the different flexing of harmonic options. You can hear me getting in almost like some sort of vocal jigsaw puzzle.”

Watch Robert Plant and Alison Krauss Perform 'Can't Let Go' from 'Raise the Roof'

Much of that education has come courtesy of Krauss, who grew up listening to tighter, more blended vocals. "It creates quite a feeling to hear him in that harmony role," she said in the same interview, "because the identity of his lead singing is so powerful. It’s a voice that’s been part of everyone’s musical experience for decades.”

Plant may be 22 years older than Krauss, but he still saw himself as a student when the pair went in to record. "I took it as an incredible challenge to be in her company," he recently told Entertainment Weekly, "because she's fascinatingly, almost slightly obsessively, desperately, remarkably capable, and I sort of come in around the corner, with a dustpan and broom, going, 'Oh, hello, I'll put my vocal on this here!'"

With more still to learn, Plant doesn't see retirement in the cards anytime soon. "Two generations from when I first started being addicted to this, I’ve still got a foot on the pedal," he said. "I’m still going somewhere. It’s the prerogative of a madman!"

Robert Plant Albums Ranked

Crafting a solo career has been something of a quest for Led Zeppelin's former frontman.