The baby is three months old.

这婴儿三个月大了。

《牛津词典》

When I was eight years old, my sister was three years old.

我八岁的时候，我妹妹三岁。

youdao

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 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

It's here that Siac fundamentally differs from the old Three Wise Men approach.

BBC: Can a spook judge the spooks?

The 17-year-old three-quarter, who made his League debut against Huddersfield in August, has signed a two-year deal with the West Yorkshire side.

BBC: Castleford hand Arundel contract

The old Three Stooges shorts were made in the nineteen-thirties and forties, and if you watch them now they look cramped, airless, and smudged.

NEWYORKER: Funny and Funnier