Hi there, Sabrina.
I'm going to make a sentence using the expression provided. The best way to learn a new word is within a sentence, I think. So, here it is:
Ex: He's still 25 and still living off his parents.
Ex: Ele tem 25 anos e ainda ''vive à custas'' de seus pais.
I think you could translate ''live off sb'' as viver à custas or depender.
Hope it helps.