[Mrs. Don-o]

In context, I don't read it as lashing out at all. At this point Peter knew he was forgiven, knew he loved and was loved, even placed in the position of "confirming the brethren" --- as shepherd of shepherds.

John was much younger than Peter. I read it that Peter may have been concerned in a brotherly (or even fatherly) way about whether John was going to be killed on the mission.

[wbarmy]

Then how do you explain Jesus’ rebuke to Peter? “What is that to you” does not seem like something one would say in answer to a brotherly or fatherly statement.