Children don't complete their set of 20 baby teeth until they are two to three years old.

孩子到两三岁时才长齐20颗乳牙。

《柯林斯英汉双解大词典》

He could find the way home though he was only three years old.

他虽然只有三岁，却能找到回家的路。

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Though the little boy is only three years old, he can dress himself.

虽然这个小男孩只有三岁，但他能自己穿衣服。

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He was fifty-three years old. J.Robert Oppenheimer and Enrico Fermi were two of the greatest scientists of the century.

VOA: special.2009.06.14

When Mike was a kid of about three years old, he was playing at his parents' garage.

迈克大约三岁的时候，一天他在父母的车库里玩耍。

斯坦福公开课 - 7个颠覆你思想的演讲课程节选

And then you remember that you moved when you were about three years old.

这时你记起大概三岁的时候，你们搬过一次家。

I used to 课堂 - SpeakingMax英语口语达人

And consider that the merger between Sanofi-Synthelabo and Aventis is not yet three years old.

FORBES: Why Bristol And Sanofi Shouldn't Merge

In the wild, tragopans do not normally breed until they are three years old.

BBC: Tragopan pheasants

The current rules stipulate one member of staff for every eight children over three years old.

BBC: Cut nursery staff to child ratio, urges minister