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John's age is affected by the same ambiguities as all beings who undergo extended voyages through space. By technical human Earth years, John is approximately 46 years old in 2557. However, during the 27 Earth years that he has spent fighting the Covenant, considerable time was spent in Slipspace. He also spent 4 years in cryo-chamber while stranded in space. The aging process is slowed in slipspace by deep sleep in cryo-chambers; in which cellular aging can be halted almost completely. Also, one could expect that individuals participating in slipspace travel might be subject to the timedilation associated with travel at relativistic speeds, so there could be more discrepancy involved there as well.
46?