This is from a scholar I do not back or trust. But this is correct
The Formation of the New Testament Canon
The Gospels cannot really be dated, nor are the real authors known. Their names were assigned early, but not early enough for us to be confident they were accurately known. It is based on speculation that Mark was the first, written between 60 and 70 A.D., Matthew second, between 70 and 80 A.D., Luke (and Acts) third, between 80 and 90 A.D., and John last, between 90 and 100 A.D. Scholars advance various other dates for each work, and the total range of possible dates runs from the 50's to the early 100's, but
all dates are conjectural. It is supposed that the Gospels did not exist before 58 simply because neither Paul nor any other epistle writer mentions or quotes them, and this is a reasonable argument as far as things go. On the other hand, Mark is presumed earlier, and the others later, because Mark is simpler, and at least Matthew and Luke appear to borrow material from him (material that is likely his own invention, cf. my review of
The Homeric Epics and the Gospel of Mark).
All the Gospels except John contain possible allusions to the destruction of Jerusalem, which was destroyed by the Romans in 70 A.D., and thus it is likely they were all written after that date.[
2] But that assumes the statements attributed to Jesus are apocryphal--they may have been genuine, the usual doom and gloom apocalyptic fantasizing, and then confirmed only by accident (or, if one is a believer, divine destiny) when the city and its temple were actually destroyed. They could also have been added to the text later. On the other hand, it has been argued with some merit that Luke borrowed material from Josephus, and if so that would date his Gospel (and Acts) after 94 A.D.[
3] Finally, there are good arguments for the existence of a lost source-text called Q which was used by Matthew and Luke to supplement their borrowing from Mark, and this has been speculatively dated as early as the 50's A.D.[
3a]
This is only an example of the state of ignorance we are in whenever scholars try to debate the dates of these writings. Although it remains possible that all the Gospels were written after 100, those rare scholars who try to place
all Christian writings in the 2nd century have nothing to base such a position on. At least some of Paul's epistles can be reasonably taken as dating no more than 16 to 32 years after the oral tradition had begun to flourish after the death of Jesus, although adulteration of those letters by later editors remains possible, and it is also possible that even in Paul's day forgeries were being made and circulated (cf. 2 Thessalonians 2:2). The Gospels were not likely to have been written down so soon, and we have clear evidence, in numerous variations, that they were altered at various points in their transmission, and scholarly work in the last two centuries has gone far to get us to the earliest versions possible.