In July 1985, David Hepworth was one of the anchors for the BBC’s coverage of Live Aid. Nearly 40 years on, he suggests that the day wasn’t just a huge charity event, but the start of a sea change in rock history. Rather than diehard music fans, it attracted an audience of “regular people”. The show’s biggest successes were largely not the “new pop” groups who’d come to prominence in punk’s aftermath, but those more experienced artists whom punk had supposedly rendered irrelevant: who’d take Spandau Ballet bullishly debuting a previously unheard track from their forthcoming album over Queen or Elton John rolling out the hits?

Here, Hepworth suggests, lurked the seeds of what he calls Rock’s Third Act, in which the belief that music is strictly a young person’s game has been subverted. It started in Live Aid’s wake, and continues to this day: vast crowds still turn out to see Paul McCartney and Bob Dylan playing live in their 80s and the Rolling Stones show no sign of quitting, 62 years into their career.

The “why” in the book’s subtitle is easily answered: because there’s still an audience and money to be made. Hope I Get Old Before I Die deals more with the “how”, via a series of snappy essays that cover everything from ageing artists’ ability to market themselves (there’s a fascinating chapter on the Grateful Dead, who managed to retain an aura of countercultural cool while flogging their fans ties and golf shirts) to the roles of sampling and social media in keeping august names part of the current conversation. They are rendered in what you might call Hepworthian style: as with all his books since 1971: Never a Dull Moment – a 2016 hit that dared you to disagree with its theory that the titular year was the greatest in pop history – its underlying principle is that the author’s youth in the 60s and 70s coincided with pop music’s solitary golden era of creativity, and that everything that’s happened since pales by comparison.

“No young person in their right mind ever thought they would be able to improve on those records that had been made so long before they were born in a world they couldn’t help feeling they missed out on”, he writes. His books read less like histories than arguments being entertainingly advanced over a pub table, and as with a lot of pub arguments, they’re big on rather sweeping statements. They also have a tendency to mix fascinating details (including one here about EMI so undervaluing the Beatles’ legacy that, in the 80s, they organised a promotion that gave their music away in exchange for Heineken ring-pulls) with rash claims that don’t bear close scrutiny. He writes that Live Aid was “one of the last unmediated experiences which music would offer” because social media didn’t yet exist. But even the most nascent social media didn’t exist for another decade, and the instantaneous Twitter response Hepworth is talking about didn’t become commonplace until nearly a quarter of a century after Live Aid: ample time for rock music to offer further unmediated experiences.

But Hope I Get Old Before I Die is never boring, largely because Hepworth is a genuinely great writer, with a winning turn of phrase – “Bob Dylan is like China. We can see what he’s doing but never work out why he’s doing it” – and a dry wit: spotting the octogenarian Paul McCartney looking stylish at a premiere provokes “the feeling that he had been closely inspected by one of the women in his life before being allowed out of the door”. He can also write movingly, as when discussing Creedence Clearwater Revival, a band so rent by decades of litigation that its founding brothers, John and Tom Fogerty, wouldn’t reconcile even when the latter was dying of an Aids-related illness.

Equally moving is the final chapter, in which Hepworth muses on his own 60-year relationship with the Beatles’ music. It has an elegiac quality: it won’t be long, he notes, until no one discussing the Beatles can actually remember their rise first-hand. Then again, Macca shows no signs of quitting in the immediate future. Nor does David Hepworth, who clearly has an audience too: largely, one suspects, comprised of his fellow baby boomers. Even if you’re not in that demographic, it’s hard not to be entertained – and occasionally infuriated – by what he does.

• Hope I Get Old Before I Die: Why Rock Stars Never Retire by David Hepworth is published by Bantam (£25). To support the Guardian and the Observer buy a copy at guardianbookshop.com. Delivery charges may apply.