Isn't "He is two days old" a valid translation?
Yes, it is. It could also refer to the amount of time one has at his disposal to do something. Example:
El are două zile (la dispoziție) ca să-și facă tema. - He has got two days (at his disposal) to do his homework.
Yes, that's the translation they were going for and the one the answer provides. I was just surprised to have my valid translation marked as incorrect by Duolingo.
So in Romanian you use has/have/a avea to indicate age, as opposed to is in English?
He has two days until what?
It means he is 2 days old, I think