According to this passage, how old was Harry when he left school?

Harry left school when he was eighteen and went to a college for a year to learn cooking. He passed his examination quite well and then went to look for work. He was still living with his parents. A lot of restaurants were looking for a cook at that time, so it was not difficult to find interesting work. Harry went to several restaurants, and then chose one of them. It was near his parents’ house. He thought, " I will walk there every morning. I won’t need to go by bus". He went to the restaurant and said to the manager; "I want to work here, but what will you pay me?" "We will pay you 30 pounds now, " the manager answered, "and 40 pounds after three months. " Harry thought for a few minutes and said, "All right, then I will start three months later. "