" When I'm Sixty-Four " is a song by the English rock band The Beatles , written by Paul McCartney (credited to Lennon–McCartney ) and released on their 1967 album Sgt. Pepper's Lonely Hearts Club Band . McCartney wrote the song when he was about 14, probably in April or May 1956, and it was one of the first songs he ever wrote. The song was recorded in a key different from the final recording; it was sped up at the request of McCartney to make his voice sound younger. It prominently features a trio of clarinets (two B♠clarinets and one bass clarinet) throughout. - source