How do you say im 11 years old in Japanese?

The most straightforward way to say "I am 11 years old" in Japanese is:

私は11歳です。(Watashi wa jūissai desu.)

* 私は (Watashi wa): I am

* 11 (Jūichi): Eleven

* 歳 (sai): years old

* です (desu): polite form of "to be"