From Bart Ehrman’s Jesus, Interrupted, pp. 144-145 (number formatting is mine):
- Even though it is very hard to date the Gospels with precision, most scholars agree on the basic range of dates, for a variety of reasons . . . .
- I can say with relative certainty — from his own letters and from Acts — that Paul was writing during the fifties of the common era . . . .
- [H]e gives in his own writings absolutely no evidence of knowing about or ever having heard of the existence of any Gospels. From this it can be inferred that the Gospels probably were written after Paul’s day.
- It also appears that the Gospel writers know about certain later historical events, such as the destruction of Jerusalem in the year 70 ce . . . That implies that these Gospels were probably written after 70.
- There are reasons for thinking Mark was written first, so maybe he wrote around the time of the war with Rome, 70 ce.
- If Matthew and Luke both used Mark as a source, they must have been composed after Mark’s Gospel circulated for a time outside its own originating community — say, ten or fifteen years later, in 80 to 85 ce.
- John seems to be the most theologically developed Gospel, and so it was probably written later still, nearer the end of the first century, around 90 to 95 ce.
- These are rough guesses, but most scholars agree on them.
Here we have in a convenient nutshell the basic reasons behind the widely accepted dates for the Gospels. Bart Ehrman explains he is not going into details here, and one can find in the literature more nuanced arguments for relative and other dates assigned to the gospels. But with these dot points we can say we are looking at the trunk of the tree.
The grounds stated for dating Paul to the 50’s seems reasonable enough. The only problem is that there is no external attestation for Paul’s letters till the second century. Ditto for the book of Acts. It is unknown until Irenaeus cites it in the latter half of the second century. That leaves only the letters of Paul themselves. How certain can we be about a date that relies solely on the self-witness of the documents themselves? Especially when we know that at the time Paul’s letters do appear they are simultaneously embroiled in controversies over forgeries and interpolations. (Marcionites accused “orthodoxy” of interpolating Paul’s letters; the letters themselves warn of forgeries, and many scholars believe the Pastoral letters are forgeries.)
But the point here is that Ehrman does supply the reasons, the evidence, for dating Paul the way most do.