In French, to express how old someone is you use "avoir [nombre] ans".
How to say how old you are in French
Look at these examples expressing age:
J'ai quinze ans.I am fifteen.
Tu as quarante ans.You are forty.
Vous avez soixante-huit ans.You are sixty-eight.
Note that to say how old someone is in French, we use avoir + age + ans.
Effectively we say I have fifteen years, not I am fifteen.
In French, you cannot omit ans as it wouldn't make sense. J'ai quinze simply means I have fifteen (fifteen what?)
To ask someone's age:
Quel âge as-tu ?How old are you?
Quel âge avez-vous ?How old are you?
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