At a promo tour for TITO, a fan asked Utada what her specific inspiration was for the song. She talked about how she noticed a lot of fresh-faced right-out-of-college kids joining the management for her label. She said she hated to see these young kids get involved in the dirty world of business politics, and this song is her way of urging them to stay gold, or preserve their innocence. The title is taken from a very popular Robert Frost poem "Nothing Gold Can Stay".
In short, it is about staying young and innocent while the world goes bad.