The lyrics "When you are young they assume you know nothing" are from the song
"cardigan" by Taylor Swift. Here is how it appears in the song: When you are
young they assume you know nothing
Sequin smile, black lipstick, sensual politics
When you are young they assume you know nothing
But I knew you dancing in your Levi's, drunk under a streetlight
... The song "cardigan" reflects on youth and the assumptions made about young
people, with vivid imagery of young experiences and emotions.
If desired, I can provide the full lyrics or more detailed context about the song's meaning.