One of the reasons that people often date the gospels after A.D. 70 is that they contain predictions of the destruction of the Jewish temple, which happened in that year.
Jesus couldn’t have predicted that event in advance, it is supposed. Therefore, the gospels had to be written after the event.
Would it surprise you to learn that Jesus wasn’t the only person to predict the fall of Jerusalem and the temple before it happened?
Or that we know this apart from the Bible?
I find your lack of faith disturbing
First things first: Jesus is God. He knows the future.
If he chooses to disclose to man part of what he sees, that’s well within his ability.
The idea that Jesus couldn’t predict the fall of Jerusalem, the destruction of the temple, or any other future event displays a lack of faith.
That is to be expected from people who don’t profess to have faith, but it is not expected from professedly Christian biblical scholars.
Why invent a postdiction?
There’s also a question of why the evangelists would make up a postdiction (a “prophecy” given after the fact).
Sure, if they wanted to paint Jesus as a prophet, making up predictions known to be fulfilled by subsequent developments would be one way to do that.
Writing after A.D. 70, they could know all about the fall of Jerusalem and–to make Jesus look like a far-seeing prophet–they could come up with a postdiction and put it on his lips.
But if that were what they were doing, they would have done it differently.