Italian gives your age with avere (to have): ho vent'anni, literally "I have twenty years". Anni is never dropped, and the question is Quanti anni hai? or, formally, Quanti anni ha?
Examples
- Ho venticinque anni.
- I'm twenty-five.
- Quanti anni ha tua sorella?
- How old is your sister?
- Mio nonno ha ottant'anni.
- My grandfather is eighty.
The mistake to avoid
"Sono venti" does not give your age - say ho vent'anni.
Where this fits in
Family & people, Italian A1: Talk about your family, say what people are like and how old they are, and introduce your friends.