"Do you have an old cat?"
Translation:A bheil seann chat agad?
There are just a few adjectives that, since the Old Irish times, tend to go before the noun, seann old is one of them (but it also, as sean, may come after the noun like a regular adjective), another would be deagh good, excellent which comes always before the noun, as in eg. deagh dhuine a good man. Or droch bad, evil which also always comes before the noun, eg. droch latha a bad day. Those adjectives cannot be used on their own (they always require a noun following them) and they lenite the following noun.