He said this to hint at the kind of death by which Peter would glorify God. And then he commanded, "Follow me."
Turning his head, Peter noticed the disciple Jesus loved following right behind.
When Peter noticed him, he asked Jesus, "Master, what's going to happen to him?"
Jesus said, "If I want him to live until I come again, what's that to you? You - follow me."
That is how the rumor got out among the brothers that this disciple wouldn't die. But that is not what Jesus said. He simply said, "If I want him to live until I come again, what's that to you?"
This is the same disciple who was eyewitness to all these things and wrote them down. And we all know that his eyewitness account is reliable and accurate.
There are so many other things Jesus did. If they were all written down, each of them, one by one, I can't imagine a world big enough to hold such a library of books.