You're at the lake feeding the ducks. But none of them want it. They know better. They've seen you before. You're bread is stale and hard as a rock. But the new duck... she doesn't know. Look! The new duck is eating bread!
That's just a grammar exercise in matching the adjective to the noun, plus at this point in the course there was very little vocabulary used so there's not much to choose from. "nowa kaczka" is as unusual as English "a new duck".
Nothing comes to my mind, apart from the fact that "starszy" (the comparative form of "stary", so literally "older") is often used with people and is considered more polite, just like "elderly" in English.