John 21:18

Verily, verily, I say unto thee, When thou wast young, thou girdest thyself, and walkest 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. Now this he spake signifying by what manner of death he should glorify God. And when he had thus spoken, he saith unto him, Follow me.

There seems to be more than a hint here that Peter's younger life had been uninhibited. He was a very active man who seems to have done just about as he pleased. Such undisciplined behavior, if that is what was implied, was at an end for Peter. His future responsibilities would require his constant attendance upon spiritual things. Also, there was a prophecy here, already fulfilled when John wrote, of the type of death by which he would glorify God.

To stretch out the hands ... was often used by Greek writers and the early Christians to indicate crucifixion.[11] In view of John's here referring these words to Peter's death, there can be no doubt of their being a prophecy of his crucifixion.

Follow me ... Jesus evidently meant this in a spiritual sense; but Peter, great literalist that he was, immediately walked after Jesus as the Lord departed, John following.

Concerning Peter's death, tradition places it at Rome in the reign of Nero, with the detail that he was crucified head downward after his protest that he was unworthy to be crucified in an upright position like Jesus. As Lanctantius wrote of Nero:

He it was who first persecuted the servants of God. He crucified Peter and slew Paul. St. Peter, as a Jew, could thus be dealt with; St. Paul, as a Roman citizen, was beheaded. Nor did he (Nero) escape with impunity; for God looked on the affliction of his people; and therefore the tyrant, bereaved of his authority, and precipitated from the height of empire, suddenly disappeared, and even the burial place of that noxious wild beast was nowhere to be seen.[12]

[11] Ibid.

[12] Lanctantius, The Manner in which the Persecutors Died (Grand Rapids, Michigan: William B. Eerdmans Publishing Company, 1951), The Ante-Nicene Fathers, Vol. VII, p. 302.