Yes, and? We know the Awoken were born during the Collapse, which occurred around 700 years ago. Let's assume our Guardian was the progeny of the first Awoken who then returned to Earth soon after the Collapse. He or she still would've been dead for centuries, which is entirely consistent with the Ghost's statement.
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So why would an awoken return to earth when it's being attacked?...
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The entire system was being attacked. It wasn't just Earth. Regardless, Earth was likely safer than living in the Asteroid Belt on ships. I imagine the early years of the Awoken were plagued by food and supply shortages, along with the constant threat of raids by Fallen etc.