Well, what I look at is "what" Jesus said to the both of them. Jesus seemed to restore Peter 3 times (as to wipe out Peter's 3 previous denials) Then Jesus says...(I will use the NKJV) John 21:18-23.
18 Most assuredly, I say to you, when you were younger, you girded yourself and walked where you wished; but when you are old, you will stretch out your hands, and another will gird you and carry you where you do not wish.†19 This He spoke, signifying by what death he would glorify God. And when He had spoken this, He said to him, “Follow Me.â€
The Beloved Disciple and His Book
20 Then Peter, turning around, saw the disciple whom Jesus loved following, who also had leaned on His breast at the supper, and said, “Lord, who is the one who betrays You?†21 Peter, seeing him, said to Jesus, “But Lord, what about this man?â€
22 Jesus said to him, “If I will that he remain till I come, what is that to you? You follow Me.â€
23 Then this saying went out among the brethren that this disciple would not die. Yet Jesus did not say to him that he would not die, but, “If I will that he remain till I come, what is that to you?â€
Peter asks about "the disciple that Jesus loved" (We know & at least agree on that this is John, one of the sons of Zebedee, the apostle of love, the one who was present at Christ's crucifixion in John 19)
So Peter inquires "what about this man?" And it is what Jesus says about John that is a prediction & a forecast just as Peter's forecast. "If I will that he remain till I come, what is that to you. You follow Me."
Now should Jesus blatantly have said, "this John here will live till I come- don't be offended that you won't & will be crucified- but I chose him for that blessed fate & not you! So mind your own business!?"
I don't think so. What is clear is what Jesus' words implied. He had to include "if I will" or His favoritism towards John would have been distracting & cold.
And what Jesus implied makes historical sense as church history says John lived to be in his 90's, into the AD90's. Well past the Second coming.