To ask someone their age in Italian, you say:
Quanti anni hai?
This literally translates to How many years do you have?
In Italian, age is expressed using the verb avere (to have), not essere (to be), like in English.
Ho ventun anni, e tu?
I’m twenty-one. How about you?
Io ho diciott'anni.
I’m eighteen.
Notice that in the last sentence, the final vowel of diciotto (eighteen) is dropped. This is done because the next word, anni (years), starts with a vowel, so it's more natural to say diciott’anni instead of diciotto anni.
You can also use the same structure to ask about someone else’s age. For example:
Quanti anni ha tua sorella?
How old is your sister?
Lei ha trent'anni.
She is thirty years old.
Again, trent'anni comes from trenta anni, but the final vowel is dropped for smoother pronunciation.
