I know many 13-year-olds who would disagree! I think you can come up with something that happened to your character at some point in his or her past. What you're trying to do is establish the character's motivations and personality. All the things that have happened to us in the past shape who we are and the decisions we make. Is the child good in school, moderate, or does he struggle? Maybe an interaction with a teacher - praise or criticism, as appropriate - would establish this. Is the child athletic or a complete klutz? How about that kickball game where the child excelled and was hauled off on the shoulders of other kids - or completely humiliated himself by falling on his face or costing his team the game? How is the child being raised? Does he live in a safe home with a loving family? How about a story about movie night and popcorn? Or maybe his home life is scary and has left him scarred. There would be many story opportunities there. Only you know the things that have happened in your character's past, because only you know your character (at least, until your novel gets published!) If you don't know about your character's past, that's the purpose of the exercise: to get to know your own character better.

Can you spend fifteen minutes on this?