I'm your age is a perfectly normal construct in English, as would be similar constructs, such as:
- You're my age.
- We're your age.
- You're our age.
- We're the same age.
- They are the same age.
- You are the same age.
Here are a few sample conversations where you might hear these. The first is a conversation between Fred, Ed, and Ed's wife Karla (who all happen to be 32):
Ed: How old are you, Fred?
Fred: I'm 32.
Karla: Oh! You're our age!
Here's a conversation between two mothers:
How old are your twins?
Oh, they're the same age as Joey. (or, Oh, they're Joey's age.)
In some cases, the word same – whether it's explicitly stated, or omitted and implied – is often used in an approximate sense, meaning "close to the same age." Imagine a man who is 37, married to a woman who is 38, talking about a new employee at the company:
A new guy started work today.
Oh, how old is he?
I'd say he's our age.
The speaker here is simply saying:
"I would guess he's in his mid- to late thirties – around the same age as us."
In this context, he's our age doesn't mean that the new employee is exactly the same age (which would be impossible anyhow, since the couple are not the same age).