Interpretation of the Stimulus

So the first part of this Stim reads: Astronomer: Earlier estimates of the distances of certain stars from Earth would mean that these stars are about 1 billion years older than the universe itself, an impossible scenario. The answer explanation that was provided paraphrased this part of it to say "earlier estimates of the distances of certain stars from Earch would have the stars be older than the universe itself" One thing that confused me on this question explanation was how you can conclude that what the Astronomer is saying is impossible is that the stars are not older than the universe. When I first read this part of the stimulus, my line of thinking was "okay so the Astronomer is saying that earlier estimates of the stars being 1 billion years older than the universe is impossible". How can we know for sure that what is impossible is the stars being older than the universe? I took it to mean that what was impossible was that the stars were not specifically 1 billion years older than the universe, rather, it could mean that for whatever reason, the stars being 1 billion years older than the universe was impossible because they are actually 2 billion years older than the universe or more, or that they are younger than the universe. Am I missing something obvious where the stimulus makes this distinction? If not, how do I avoid this kind of error in the future?