Albert Barnes Commentary John 21:18

"Verily, verily, I say unto thee, When thou wast young, thou girdedst thyself, and walkedst whither thou wouldest: but when thou shalt be old, thou shalt stretch forth thy hands, and another shall gird thee, and carry thee whither thou wouldest not." — John 21:18 (ASV)

When you were young. When in early life you girded yourself and went where you wished. The Jews, in walking or running, girded their outer garments around them, so that they might not be impeded.

You girded yourself. The expression here denotes freedom. He did as he pleased—he girded himself or not; he went or remained, as he chose. Perhaps the expression refers more to that time than to the previous period of Peter's life: "You, being young or in the vigor of life, have just girded yourself and come freely to the shore." In either case, the Savior intimates that at the end of his life he would not be so free.

When you shall be old. Ancient writers say that Peter was put to death about thirty-four years after this. His precise age at that time is not known.

You shall stretch forth your hands. When Peter was put to death, we are told that he requested that he might be crucified with his head downward, saying that he who had denied his Lord as he had done was not worthy to die as He did. This expression of Christ may intimate the readiness of Peter thus to die. Though he was not at liberty as when he was young, though bound by others, yet he freely stretched out his hands on the cross and was ready to give up his life.

Another shall gird you. Another shall bind you. The limbs of persons crucified were often bound instead of being nailed, and even the body was sometimes girded to the cross.

Carry you where you do not wish to go. This means another shall bear you, or shall compel you to go to prison and to death. This is not said to intimate that Peter would be unwilling to suffer martyrdom, but it stands in contrast to the freedom of his early life. Though willing when compelled to do it, yet he would not seek it; and though he would not needlessly expose himself to it, he would not shrink from it when it was the will of God.

Compare another shall gird you with Acts 21:11.