九岁的英文怎么说怎么写

"九岁"的英语表达是 "nine years old"。其中 "nine" 是数字"九"的英文表达，"years" 是"年"的英文表达， "old" 是"岁"的英文表达。

例句：

My son is nine years old.
我的儿子九岁了。

She is a nine-year-old girl.
她是一个九岁的女孩。

He is just nine years old but he already knows how to read and write.
他才九岁，但已经会读写了。