He was about twelve or thirteen years old at the time.

　　那時候他大概十二、三歲左右。

　　I was thirteen years old then.

　　那時的我才十三歲。

　　I was this height when I was thirteen years old, which is really hard.

　　我十三歲就長了這么高，太痛苦了。

　　I am tall, dark hair, blue eyes, thirteen years old.

　　我是高大的、深色頭發、藍眼睛、十三歲。

　　This boy is thirteen years old.

　　這個男孩十三歲。