Of course it relies on who's writing the story.. I don't like that answer as it's the answer to ALL ambiguous fluff questions.
Luther and Kor Phaeron are good examples, but they were upgraded 10.000 years ago, while the Emperor was still alive - while geneseed was still understood fully..
How long can an average human live if he gets augmentations in 40k? I know that some of the warmasters (macharius, slaydo) easily lived beyond their hundreds