他12岁用英语可以说是："He is twelve years old." 来源：这句话的来源是一般用来表达一个人的年龄的语法结构。

下面是一些例句：

My son is twelve years old.

She is twelve years old and in the seventh grade.

We celebrated his twelfth birthday last week.

希望这些信息能够帮助到您！