Written between a.d. 85–90 from Ephesus, after the destruction of Jerusalem (a.d. 70) and before John’s exile to the island of PatmosThe Gospel of John contains no references concerning where it was written. But according to the earliest traditions of the church, John wrote his Gospel from Ephesus.
That church is described in Revelation 2:1-7.We don’t know how old John was when Jesus called him. But assuming that John was a little younger than Jesus, John would have been in his eighties when writing this Gospel, quite old for a time when the life expectancy was much shorter. And considering the fact that all the other apostles had died as martyrs, John was indeed the church’s elder statesman. We can imagine him teaching and counseling the Christians in this well-established church, as well as doing some writing.