According to the story, McCartney wrote this song when was 16 and forgot about it until his father turned 64, which happened to be as the Beatles were recording 'Sgt. Pepper's Lonely Hearts Club Band.

But I’m here now. Just turned 64 a few weeks ago and must say it has already caused a bit of confusion. It started when my dear school friend sent me a New Year’s card that said what a great time was ...