Yes, the verb "Has" is used with the third person (he, she, it), its primary meaning is “to possess, own, hold for use, or contain.” When you say your years old must to use "verb to be" In English we use TO BE for your age and not have as in some other languages. (In Spanish you use tener -have/has-, In French avoir , in Italian avere, but in English we do not use have, we use to be).

The correct way is: He is seventeen years old.

Yes