Read the following conversation and answer the question.

M: Congratulations on breaking the records at the recent Olympics, Miss Green!

W: Thank you, Mr. Rarker.

M: Oh, look at those trophies! You became a swimming star at the age of fifteen, didn't you?

W: Yeah, you're right.

M: Could you tell me something about your plans for the future?

W: To tell you the truth, I'm going to give up swimming from now on.

M: I beg your pardon?

W: I mean I'd rather not swim at all. I'm too old to...

M: Excuse me, if I'm not wrong, you've only twenty now. Is it too old at twenty?

W: Yes, too old for a swimmer. If I swim in an international competition, I'll hardly be able to win.

M: But...er...don't you enjoy swimming?

W: Certainly, and I enjoy visiting other countries, and the Olympics are very exciting. However, I missed more important things. I had to work very hard at swimming. There was training before school, after school, and at weekends. While other girls were growing up, I was swimming, swimming. But life isn't merely swimming, is it?

Question: When did Miss Green become a swimming stars 

- At the age of 15.

- At the age of 20.

- At the age of 18.


At the age of 15.