Paul McCartney has spent decades crafting some of the most beloved songs in music history, but even legends have regrets.

When looking back at ‘When I’m Sixty-Four’, one of his earliest compositions for The Beatles, McCartney admitted that he may have made a mistake in the lyrics.

The song, a whimsical ode to growing old together, was written when he was still a teenager - far from the reality of aging. And now, as time has marched on, he has a different perspective on what he should have done differently.

‘When I’m Sixty-Four’ first appeared on Sgt. Pepper’s Lonely Hearts Club Band in 1967, but McCartney originally wrote it in his late teens, inspired by the jazz and music hall style that his father loved.

And despite the song’s warm reception, McCartney later admitted that the number in the title, 64, was somewhat arbitrary.

In an interview with the Los Angeles Times in 2006, McCartney suggested that he should have chosen a slightly older age.

“It was really an arbitrary number when I wrote the song. I probably should have called it ‘When I’m 65,’ which is the retirement age in England,” he said. “And the rhyme would have been easy - ‘something, something alive when I’m 65.’”

So why didn’t he change it? Simple: he felt ‘When I’m Sixty-Four’ had a better ring to it.

“But it felt too predictable,” he explained. “It sounded better to say 64.”

On the other hand, John Lennon, McCartney’s legendary songwriting partner, never shared Paul’s thoughts that originated the song.

“[That is] Paul’s [song] completely,” Lennon said in All We Are Saying: The Last Major Interview With John Lennon and Yoko Ono by David Sheff. “I would never even dream of writing a song like that. There’s some things I never think about, and that’s one of them.”

At 82 years old, McCartney has joked about how outdated the song now seems. He once recalled a conversation with a pianist who played music for senior citizens and had to make an adjustment to ‘When I’m Sixty-Four’ to keep it relevant to his audience.

“I met someone who plays piano in an old persons’ home, and he said, ‘I hope you don’t mind, but I play some of your songs, and the most popular one is When I’m Sixty-Four, but I have to change the title to When I’m 84 because 64 seems young to those people. They don’t get it,’” McCartney shared.

“If I were to write it now, I’d probably call it When I’m 94,” he joked.