John the Apostle
John 21:18ESV·traditional attribution

Truly, truly, I say to you, when you were young, you used to dress yourself and walk wherever you wanted, but when you are old, you will stretch out your hands, and another will dress you and carry you where you do not want to go.”

John Calvin Reformed @genevareformer

18. Verily, verily, I tell thee. After having exhorted Peter to feed his sheep, Christ likewise arms him to maintain the warfare which was approaching. Thus he demands from him not only faithfulness and diligence, but invincible courage in the midst of dangers, and firmness in bearing the cross. In short, he bids him be prepared for enduring death whenever it shall be necessary.

Matthew Henry Presbyterian @wholebiblehenry

We have here Christ's discourse with Peter after dinner, so much of it as relates to himself, in which, I. He examines his love to him, and gives him a charge concerning his flock, Joh 21:15-17. Observe, 1. When Christ entered into this discourse with Peter.

Commenting on John 21:15-19

John Gill Reformed Baptist @doctorgill

Verily, verily, I say unto thee,.... A way of speaking often used by Christ, when about to deliver anything of considerable moment, partly to raise the attention, and partly for the more strong asseveration of what is spoken; and may have reference both to what went before, confirming Peter's declaration of his love, which would be demonstrated by dying for him, and the testimony of...