This small faded papyrus fragment of John 18:31-33 which is dated 125 CE is
the earliest known copy of any of the gospels.
Source: Robert J. Miller, Editor, The Complete Gospels: Annotated Scholars
Version, rev. & expanded ed. (San Francisco: HarperSanFrancisco, c1994), p. 7.
John is still thought to be the last gospel to be written but at a date much too late to have been the work of an original disciple. Although the gospel acknowledges that Jesus and his disciples were Jews, the opponents of Jesus are generally categorized as "the Jews." John's gospel seems to be addressing a particular social situation where Christians are in strong opposition with Jews which would be typical of the years 90 CE or later. John rarely mentions the most powerful Jewish party of the Sadducees (high priests) so prevalent in the other gospels that had died out when Jerusalem was destroyed in 70 CE but John rails against the Pharisees which is the party that survived the destruction and went on to form what is now called Rabbinic Judaism.
Judaism of the first 70 years of the first century CE permitted many possible interpretations of God's message; but, following the destruction of the Temple, Jewish leaders began to close ranks and prescribe what were and were not correct Jewish beliefs. Christians were being thrown out of the synagogues for their lack of adherence to prescribed Jewish orthodoxy and this may have led to the hostility towards Jews being expressed in the Gospel According to John.
Most scholars speculate that John was written between 90 and 95 CE in an unknown place and by an unknown person.