If you ask to me: "How old are you?", is it correct I answer:"I' m sixteen.", or I need always to say "years old" in the final?

Why, after all, am I asking this? Because I'm a Brazilian teenager and because I know that if you ask to me: "how old is your notebook?" I need to answer " It's two years old", and not: "It's two.". With persons, is it the same thing? Thank you very much for your... show more Why, after all, am I asking this? Because I'm a Brazilian teenager and because I know that if you ask to me: "how old is your notebook?" I need to answer " It's two years old", and not: "It's two.". With persons, is it the same thing?
Thank you very much for your attention!
Happiness! =)
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