几岁

wǒ zhī dào tā jǐ suì

我知道她几岁。

I know how old she is.

nǐ jīn nián jǐ suì le

你今年几岁了？

How old are you?

zhè ge xiǎo péng yǒu jǐ suì le

这个小朋友几岁了？

How old is this kid?