It's something like possession. when you " have " something, you can feel it,touch it, smell it, taste it. but when you "are " like something, you possess the quality of that thing. for example: when you say, you are polite. it means, you have the quality of politeness. while you can't touch, taste,smell the politeness. after all, we have thing that we can find it through our five senses.

Actaully we dont know ... old rule also the french say that j ai 17 = i have 17

It's more common to use verb to be, so you have to say it in that way when communicating with other people.

Correction: What is the right way of saying my age ? I am 19 years rather than I have 19 years. You would say 'I am 19' There is no need to add the word 'years' that is understood by the listener.

Thanks, guys!!!