What does the light-travel time of a star's light reaching Earth NOT represent?
Answer
The star's true age (duration since its birth)
A critical distinction must be made between light-travel time and stellar age. If a star's light takes 500 million years to reach Earth, we are observing the star as it existed 500 million years in the past—that is the light travel time. However, the star itself was already formed and fusing hydrogen for some duration *before* that light began its journey. The true age is the total duration from the star's birth until the present moment, regardless of how long its emitted photons took to traverse the distance to the observer.
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