Once Upon A Long Ago by Paul McCartney is a nostalgic song that reflects on the passage of time and the innocence of youth. The song reminisces about a simpler time, filled with fairy-tale like memories and a sense of wonder. Key themes include nostalgia, youth, and the bittersweet nature of growing older. Particularly poignant moments in the song are the vivid descriptions of carefree childhood adventures and the longing for the simplicity of those days.