During the Enlightenment, critics sought to discredit the New Testament by claiming that it was written during the 2nd Century, thus making it an unreliable testimony to the life and teachings of Jesus. That became the consensus among liberal scholars, as they tried to pick apart the Scriptures and reduce it to myth and legend. But as the liberal Anglish Bishop John Robinson point out a generation ago, then when he decried to look at the evidience with “new eyes” he concluded that a dating before the Destruction of the Temple was as likely as a later dating, even perhaps for John’s Revelation. Skeptics are seldom impartial, and may be true-believers. When we flee one room, we usually not pass into another, and then bar the door behind us, never again to open it and look at what impelled us to flee.
(I also believe the Fourth Gospel was written by an eyewitness to Jesus' ministry, but that is another story)
The fact that the destruction of Jerusalem in 70 AD wasn’t even hinted at in the books of the New Testament is the most powerful evidence that they were written before that time. This was a pivotal event in Jewish history, and it would have been hard for Jewish writers writing about time to ignore it.
As an analogy, think of someone writing about and events in 20th century Germany, and making no reference to WWII. Even if you are writing about 1910 or 1990 Germany, at some point a reference to WWII would probably work its way in.