In English, when somebody asks you how old you are, you probably answer with something like: “I am 35.” If you literally translate that to French, it would not make sense for two reasons:
In French, the verb we use is “to have.”
You always need to add the word “years” after the number.
So instead, you would say “j’ai 35 ans” (I have 35 years).
Quel âge as-tu ? J’ai 42 ans – literally translates to: What age have you? I have 42 years.
Quel âge a Madonna ? Madonna a 56 ans – literally translates to: What age has Madonna? She has 56 years.