我今年12岁了用英语怎么说高级句式

"I am 12 years old" 的高级表达方式是 "I have reached the age of 12."

这种表达方式来自于英语中经常使用 have reached 表示达到某个年龄。

例句：

I have reached the age of majority. (我已经达到了法定年龄。)
He has reached the age of retirement. (他已经达到了退休年龄。)