1.基数词表示年龄
My son is twenty-one.我儿子21岁了。
Her daughter is eighteen.她的女儿18岁。
2.基数词+years old/years of age
Her daughter is eighteen years old.她的女儿18岁。
her daughter is eighteen years of age.
3.at the age of+基数词
My son is at the age of twenty-one.我儿子21岁了。
Her daughter got married at the age of twenty eight.她的女儿28岁结的婚。
4.合成词“基数词+year+old”
My 21-year-old son was in the army.我21岁的儿子入伍了。
Her 18-year-old daughter is now in the university.她18岁的女儿正在上大学。
【提示】 合成形容词中名词不用复数，如这里的year就用单数形式。
5.of+基数词
My son is a soldier of twenty-one.我儿子是一个21岁的士兵。
Her daughter is now a pretty girl of 18.她女儿现在是一个18岁的美少女了。
6.aged+基数词
I have a daughter aged 13.我有一个13岁的女儿。
Lying on the floor was a boy aged about seventeen.
躺在地板上的是一个约莫17岁的男孩。