What context and time is Jesus talking about when he mentions this?

Christ was referring to the manner of death that Peter would face for his faith. Peter would be led by the hand as an old man to be crucified just as Jesus was crucified. But Peter requested that he not be executed in the same manner that Jesus was because he felt that he was not worthy to die in the same manner. Therefore Peter was crucified Up-Side-Down. He was led by the hand to a place where he would not go himself. Who led him there is a matter of depth of christian maturity that most cannot understand or accept. It is a question for only the most mature christians to receive.