13 years I think it was before the hardcoded limit kicks in. You must
really like wandering around though, I never reached the limit even when I tried.
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Unless... Was it just FO1 that had the bug with newer computers where the movement in world map was sped up by a huge degree? If it's happening in your game in FO2 as well, reaching the 13 year limit would be relatively easy to reach by just wandering around the wastes.