ages

1 use of be

We most often talk about people's ages with be + number

He is thirty (NOT he has thirty)

 or be + number + years old (more formal: ... of age).

He is thirty years old / of age. (NOT thirty years.)

We ask How old are you?, not normally What is your age?

2 be + ... age

Note the structure be + ... age (without a preposition).
When I was your age I was working. (NOT when i was at your age)

The two boys are the same age. She's the same age as me.

3 prepositions

In other structures, at is common before age.
He could read at the age of three. (NOT  in-the-age ) At your age 1 already had a job.

 for more details click here http://en.wikipedia.org/wiki/English_language 

or  http://blog.myhappyenglish.com/2011/12/28/english-lesson-talking-about-age/