There are a number of data which strongly suggest a date in the 60s, chief among them are the following.
(1) The destruction of Jerusalem is not mentioned. This fits extremely well with a date before 66 CE.
(2) The topographical accuracy of pre-70 Palestine argues that at least some of the material embedded in the gospel comes from before the Jewish War.
(3) There is much primitive terminology used in this gospel. E.g., Jesus’ followers are called “disciples” in John, not apostles.
(4) The conceptual and verbal parallels with Qumran argue strongly for an overtly Jewish document which fits well within the first century milieu.
(5) The date of P52 at c. 100-150, coupled with the date of Papyrus Egerton 2 at about the same time—a document which employed both John and the synoptics—is almost inconceivable if John is to be dated in the 90s.34
(6) John’s literary independence from and apparent lack of awareness of the synoptic gospels argue quite strongly for an early date. Indeed, this independence/ignorance argues that all the gospels were written within a relatively short period of time, with Matthew and Luke having the good fortune of seeing and using Mark in their composition.
(7) Finally, there is a strong piece of internal evidence for an early date. In John 5:2 the author says that “there is in Jerusalem, by the sheep-gate, a pool (the one called Bethesda in Hebrew) which has five porticoes.” Without discussing all the interpretations possible for this verse suffice it to say that (a) the verb “is” (ἐστιν) cannot be a historical present, and (b) the pool was destroyed in 70 CE.35 By far the most plausible conclusion is that this gospel was written before 70 CE.
In sum, we believe that a pre-70 date for the Fourth Gospel is the most probable one. Further, we believe that this gospel should be dated late in 65 or even in 66, for the following two reasons: (a) it is doubtful that it should be dated after 66, because otherwise the lack of an Olivet Discourse in which many of the prophecies were at that time coming true, is inexplicable; (b) the gospel should perhaps be dated after Peter’s death, as we shall see when we examine the purpose.