The police are concerned for the safety of the 12-year-old boy who has been missing for three days.

那个12岁的男孩失踪三天了，警方对他的安全感到担忧。

《牛津词典》

It is incredible that the 12-year-old managed to even reach the pedals, let alone drive the car.

这个12岁的小孩能够得着踏板都令人难以置信，更不用说开汽车了。

《柯林斯英汉双解大词典》

A 12-year-old might need to be shown that raiding the biscuit tin without asking permission is acceptable, but that borrowing a parent's clothes without permission is not.

一个12 岁的孩子可能需要人告诉他，未经许可就把饼干盒扫光是可以接受的，但是，未经许可就借用父母的衣服是不能接受的。

youdao

Rebecca Estepp of San Diego, has a 12 year old son with autism.

VOA: standard.2010.03.23

The study was, eleven- and 12-year-old boys at a camping program.

实验中有一些11，12岁的男孩,参加一个野营活动。

耶鲁公开课 - 心理学导论课程节选

I'm 12 years old and I resolve to get a girlfriend this year.

VOA: special.2009.01.01