Whom can we adress this way? Animals, because they are neuter?
It's a substitute for any word that is a neuter plural. For example města ('cities'), zvířata ('animals'), kuřata ('chickens'), kůzlata ('goatlings', 'goat kids') etc.
i don't understand it says that it is are they but said the correct answer is they are please reply thanks
Would jsou to stará also be acceptable?
Not really. It would be acceptable if you added a noun at the end of your sentence, e.g. animals - Jsou to stará zvířata. This would be correct.