Fallout 4's prologue sequence ends with the protagonist heading into Vault 111 as the bombs drop in 2077, and emerging 200 years later (the same time period in which Fallout 3 is set), his wife and baby presumed dead given that he's been referred to as the "sole survivor". Bethesda said they deliberately weren't divulging anymore plot details for now in order to preserve the mystery, causing fans to wonder: how the hell can a guy not age for over 200 years? The obvious answer, of course, is some sort of suspended animation or cryogenic storage system contained within the Vault, which given the series' tone wouldn't exactly be outside the realm of possibility, and it's certainly more plausible than time travel. You'll probably be waiting a while to know the truth for sure, though.