Read the following text about Bill Gate, the co-founder of Microsoft, and choose the best answer.

Bill Gates is the co-founder of Microsoft, the world’s largest PC software company. He is among the richest people in the world. Bill Gates’ interest in computers started when he was a teenager. After high school, he was accepted to several top colleges in the USA: Harvard, Yale, and Princeton. He chose to go to Harvard to study law. At Harvard, he focused more on his interest in computer than on coursework. He often relaxed by playing video games in Harvard’s computer lab. He left Harvard before graduating because he wanted to open a software company with his friend Paul Allen. However, he later said, “ I don’t think dropping out is a good idea.” In 2007, he received an honorary degree from Harvard. He began his speech by saying this to his father in the audience. “I’ve been waiting more than 30 years to say this: Dad, I always told you I’d come back and get my degree.” Bill Gates is no longer working full time for Microsoft. He is now, with his wife, running The Bill & Melinda Gates Foundation which aims to improve healthcare, reduce poverty, and promote education around the world.

When did Bill Gates first develop his interest in computers?