And what about “Antichrist” usually termed “THE Antichrist”?
First of all the Bible does not explicitly state there is an Antichrist (singular). According to John this may have been a confusion already in his time:
18, Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time.
19, They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
Notice that not only John corrects a misunderstanding but that he also uses the present tense. The presence of many antichrists show that, at the time of this writing, AD 61-62, it was already “the last hour” (YLT)*
The falling away is the apostasy of the Jews who had previously professed the faith. Their defection was not immediately apparent, just like tares among wheat are not immediately obvious. What made it the “last days” was a persistent and long-lasting turning away from the truth. And these lands, Judea and through much of the Diaspora, had great exposure to the Truth, Those finally settling down into a hatred for the New Wine were exactly the people these later epistles (John, Jude, Peter, Pastorals) are addressed to.
The Man of Sin possibly could be Nero. That would fit the description pretty well.He certainly was a moral mess. But his sinful life was fairly well hidden at first. This was partly because of the better influences of his mother and wife, and his teachers Seneca and Burrus. But after a few years the real Nero came out. In a few years he killed all these people. It might very well be that Seneca was the restrainer that Paul had in mind in 2 Thess. 2:7:
“For the mystery of lawlessness is already at work; only He who now restrains will do so until He is taken out of the way.”
Another possibility (more likely, I think) is Eleazar Ben Ananias. He gained the ascendancy in the Temple when he killed his own father, Ananias of Acts 22. He would have been the restraining influence. Interestingly, Paul had said eight years earlier, “God is about to strike you, you whitewashed wall!” It was right after the death of the father that the son “went off on a nut”. You can read all about it in Josephus.
NOTE: According to some we have been in the last days – and last hour – for almost 2 thousand years. Does that make sense? The whole period of the Jewish Dispensation, from Sinai to the 1st century AD, is only 1,500 years.