He was about twelve or thirteen years old at the time.
那时候他大概十二、三岁左右。
I was thirteen years old then.
那时的`我才十三岁。
I was this height when I was thirteen years old, which is really hard.
我十三岁就长了这么高，太痛苦了。
I am tall, dark hair, blue eyes, thirteen years old.
我是高大的、深色头发、蓝眼睛、十三岁。
This boy is thirteen years old.
这个男孩十三岁。