Note 17 at Joh 21:23: John was writing this Gospel around the end of the first century (see Life for Today Study Bible Notes, Introduction to John, Date of Writing), and he included this information to correct a misunderstanding of Jesus' statement, that he had probably heard many times. Apparently, some people had interpreted Jesus' comments to Peter to mean that John would not die before the second return of Jesus. However, John made it clear that Jesus didn't say that. Jesus simply stated to Peter that if He willed that John remained alive until He comes again, that should not affect the way Peter followed Him.