'Age' is a noun (sustantivo) - 'edad' in Spanish.

So you could say;

'What is your age?'

'John and Paul are the same age'.

Cuando era pequeño is translated most directly and usually as... When I was a child. 

The above posts about the word age is correct. It is both a noun and a verb. Edad = the noun age and envejecer = the verb to age.

To add to the previous comment, "age" as a verb means "to get older" so it would translate either as crecer or envejecer

"As we age, we do not hear as well."

I've just seen your added note.

Yes, 'age' can be a verb, but you need to use it with the actual age (number of years), not with a general word like 'small'.

For example :   'Most children start school aged five or under'

This means 'when they are five years old.'

This use of 'age' is quite unusual, though.

Cuando era pequeño? means "When I was small/little"