This wasn't my belief, but rather that of a very young piano student of my mother's. The student was practicing a transcription of a piece by Georg Philipp Telemann, and Mom thought the student might be interested to know just how long this music has been with us. She pointed to the dates 1681-1767 under the little picture of the composer with his powdered wig and told the student that that's when he lived, so this piece was around 300 years old. The student said, "Oh... I thought that was his phone number!"
A childhood belief about songs

others believed things like this
- I thought that a "student visa" meant to use a credit card while travelling.Anon
- My music teacher once said that music in an electrical piano was made by little tiny men that lived inside it.Anon
- I thought Spongebob Squarepants was a piece of Swiss cheese.— Melanie
- i used to believe that one piece of ear wax was actually called a wach. — rachael
- I used to think that a gherkin was some kind of piece of machinery. I wonder where I got THAT from...— Some Idiot
- I used to believe fax machines instantly teleported a piece of paper to who ever you wanted. Anon