How do you say i am eleven years old in mandarin?

There are a couple of ways to say "I am eleven years old" in Mandarin, depending on the context and level of formality:

Formal:

* 我今年十一岁。 (Wǒ jīnnián shíyī suì.) - This is the most common and formal way to say it. It literally translates to "I this year eleven years old."

* 我今年十ー岁。(Wǒ jīnnián shíyī suì.) - This is the same as above, but uses the traditional character for "one".

Informal:

* 我十一岁。 (Wǒ shíyī suì.) - This is a more casual and direct way to say it, literally translating to "I eleven years old".

You can also use the word "岁数" (suìshù) which means "age" in a sentence like this:

* 我岁数是十一岁。 (Wǒ suìshù shì shíyī suì.) - This is a less common way to say it, but it is still grammatically correct.

Note: When you say your age in Chinese, you don't use the word "years" (年 nián). You just use the number and the word "岁" (suì) which means "years old".