Portuguese gives your age with ter (to have): tenho vinte anos, literally "I have twenty years". Anos is never dropped, and the question is Quantos anos tens? or, formally, Quantos anos tem?
Examples
- Tenho vinte e cinco anos.
- I'm twenty-five.
- Quantos anos tem a tua irmã?
- How old is your sister?
- O meu avô tem oitenta anos.
- My grandfather is eighty.
The mistake to avoid
"Sou vinte anos" is wrong - age uses ter: tenho vinte anos.
Where this fits in
Family & people, Portuguese A1: Talk about your family, say what people are like and how old they are, and introduce your friends.