When he was 16, Jack Browne sat down at his parents’ kitchen table in Fullerton, Calif., and started picking out a tune on an old Kay guitar.

It was the fall of 1964, and the fledgling songwriter and high school junior — inspired by books, records and his own suburban disaffection — began weaving together an existential number about loss and regret called “These Days.”

It would be a year until he finished the song, nearly a decade before he recorded it properly. By the time Jackson Browne, as he would be known professionally, cut it for his 1973 album “For Everyman” — which will be reissued on Sept. 20 — it had already been done in two distinct, definitive versions: the first by the German chanteuse and Velvet Underground collaborator Nico, then later by the Southern rocker Gregg Allman.

“These Days” has proved a remarkably durable composition, reinterpreted by Cher, St. Vincent, Glen Campbell, Miley Cyrus, Paul Westerberg and Drake, to name a handful. It inspired Wes Anderson’s 2001 film “The Royal Tenenbaums,” and more recently has become the unlikely soundtrack to a series of TikTok trends.

While Browne has had bigger hits as an artist (“Doctor My Eyes,” “Running on Empty”) and as a writer (Eagles’ “Take It Easy”), “These Days” has rambled through the decades, morphing musically, changing lyrically and taking on added layers of meaning. “In that regard, it’s sort of like a folk song,” Browne said on a late August afternoon, sitting in the control room of his Santa Monica recording studio, Groove Masters.

“I come from folk music, that was my school,” continued Browne, somehow still boyish and bright-eyed at 75. “You’d learn several versions of the same song and adapt the parts of it that you liked and it’d become something else. That’s what’s happened with ‘These Days.’”