“In very truth I tell you, when you were young you regularly dressed yourself and walked where you wished, but when you will be old you will stretch out your hands and another will determine your dress and carry you where you do not wish to go.” Now this he spoke signifying by what manner of death he would glorify God.'
Peter had been free and was free now to do what he wished. But he was warned that one day he would be in the hands of the authorities and would be forced to do what they wanted, and their purpose would be to take him to prison and execution. There may be a hint here that that death would be by crucifixion, (some non-Biblical writers did use the term ‘to stretch out the hands' as indicating crucifixion) but not necessarily so. The stress was on physical helplessness and violent death. Just as he had seen Jesus seized and led off to death, the death Peter had sought to avoid by his denial, so would it be with him.
There is an interesting contrast here with what Jesus had said about Peter denying Him. There too His statement began, ‘in very truth' (John 13:38). Both situations were inevitable due to the weakness of man and the purposes of God. Satan was allowed to lead Peter astray, but only under the final protection of God (Luke 22:31). In the end he would be restored, having learned the lesson through which he would be able to help others. And in the end his restoration would be finally completed when he experienced readily what his denial had sought to prevent.