Is the question of "what age are you" idiomatic,common or does it
sound naturally in the meaning of " how old are you "
Can we say this structure could be used for materials as " how age is
it "
"What age are you?" is definitely not idiomatic. Using it would mark you instantly as a non-native speaker. However, it makes logical sense and it would be understood.
"How age is it?" would be even worse. While most native speakers could likely figure out what this meant, it sounds simply wrong.
If you were asking a person about his or her age, you'd almost always say "How old are you?" or "What year were you born?" or "When were you born?" -- with the first one being by far the most common.
If you were asking about an object, you would usually say "How old is it?" But you might also say "When was it built?" (in reference to a building or structure) or "How long has it been here?" or "How many years has it been here?" or "How long has it been around?" -- again, the simple "How old is it?" would be most common.
Best Answer
In any spoken English How old are you is far, far more natural than what's your age. So, if you don't want people to notice your stilted English, it is far better to use How old are you?.
It might also be helpful to know that we don't usually use the words years old in the reply. We just state the number. And it's actually ungrammatical to say just years:
There may be special circumstances when someone might say What's your age?, but the normal question is How old are you?. The answer is "(X)", not "(X) years", or even "(X) years old" - unless you are five!