Soon thereafter, rock and roll became Paul's new passion, but he never forgot his fondness for the music he had grown up with. When the Beatles' amplifiers sometimes broke down at the Cavern or in Hamburg, Paul would sit at the piano and pull out When I'm Sixty-Four as a sort of novelty number, and it went over surprisingly well with both the crowds and his bandmates.
In late 1966, the Beatles spent several days working on one of their most experimental pieces, Lennon's Strawberry Fields Forever. Once that recording was considered complete, McCartney opted to go in a completely different direction, and they revived this old-fashioned chestnut on December 6th with two takes of Paul on bass, Ringo on drums and John playing just a little bit of electric guitar. Paul then overdubbed a piano track as Ringo added some more subtle drum work with his brushes. Two days later, on December 8th, Paul recorded his lead vocal. The 50th anniversary edition of Sgt. Pepper's Lonely Hearts Club Band presents the song as it stood at this time in its stripped-down form.
The group then worked on a remake of Strawberry Fields Forever over several sessions before returning to When I'm Sixty-Four on December 20th. On this date, Paul, John and George sang the charming background vocals while Ringo added yet another percussive element - tubular bells - which are struck at a few selective points in the song.
Paul had clearly met with producer George Martin before the next day, December 21st, to discuss the final touch - an overdub of clarinets, two regular and one bass. Martin's arrangement is brilliant, bringing an old vaudeville, music hall, or "rooty-tooty" feel to the number, as Paul requested. Though Paul had yet to come up with the Sgt. Pepper concept on this date, this is the song that manages to fit most perfectly into that imaginary world.
And yet, it almost wasn't on the album at all. When Capitol Records pressured manager Brian Epstein for a new single from the Beatles, When I'm Sixty-Four was proposed as the B-side to Strawberry Fields Forever. The only other song which was complete at the time was Penny Lane, and it was ultimately chosen instead for what turned out to be a double A-sided single.
When I'm Sixty-Four sits in the second slot on side two of Sgt. Pepper, immediately after George Harrison's Indian-flavored Within You Without You, thus providing the greatest contrast on the album. The song also sounds rather fast, as it was sped up during the mixing process, bringing it up almost a semitone.
The song was chosen for an amusing sequence in the animated film Yellow Submarine, in which the boys and Old Fred rapidly age, growing huge white beards, then just as quickly get young again. It therefore appeared on the 1999 release known as the Yellow Submarine Songtrack.