On pages 181-193, what time did Daniel remember when he was with his sister?

Daniel remembers a time when his sister was 12 and he was 17. He was sitting on the windowsill of her room. Even though he was older, he felt younger than his sister because she was so brilliant. She was always reading. He thought about how they had fought all summer long. He remembers how he and his father were going back to school in England the next day. In the years before, he had been her hero. However, at that point in time she did not like him and just rolled her eyes when he told her jokes.