Here's the BIBLICAL truth of the matter:
(1) The "Temple of God" to which Paul is referring is the one that was erect in Jerusalem at the time he is speaking. That was God's temple to the Hebrews since the times of Solomon, and it was still standing.
(2) The man of sin was alive at the time Paul is speaking (2 Thess 2:7). His accomplices in his work of rebellion were the "sons of disobedience" (Eph 2:2; Eph 5:6; Col 3:6), Judaizers who were set apart to receive God's wrath for their persecution of the apostles that were spreading the gospel of Christ to all the gentiles (1 Thess 2:14-16; Eph 5:6; Col 3:6). Judas,
a member of the Zealots, had been a part of this political movement, and thus was called "son of perdition" (Jn 17:12/2 Thess 2:3). Judas was acting along with this key political movement when he betrayed Christ to the rulers.
The Zealot movement was a violent terrorist movement, and it took over the Temple in AD 66 [the Sicarii (dagger-men terrorists)], launching the Jewish Civil War and Great Revolt against Rome that ended in the destruction of the Temple, Jerusalem, and most of Israel's cities.
(3) The Thessalonians knew the person or political force at the Temple that was restraining the man of sin from taking it over for himself and his militia at the time Paul wrote (2 Thess 2:6).
(4) The Thessalonians were to expect the man of sin to overcome the resistance at the Temple and take it over. Once that event took place, the Thessalonian persecution was close to over (2 Thess 1:4-7/Acts 17:1-8). All the Judaizers of the Empire had made pilgrimage to Jerusalem for the Mosaic spring festivals (Deut 16:16/Ex 34:23-24/Ex.23:17) when the Romans came and trapped everyone inside the city then leveled it with "all its children inside" (Lk 19:43-44; Mt 24:1-3)
So, As to the "man of lawlessness/the son of perdition," scripture makes it clear that he was being restrained from siezing control of Herod's Temple in Jerusalem at the time Paul was writing to the Thessalonians (see: 2 Thess 2:6-7). The passage itself shows He was already a blood pumping, air-breathing, grown Human MAN at the time Paul wrote the passage, and the Thessalonians already knew who was restraining him from his takeover of the temple. This man's lawlessness was already at work in the nation of Israel in Paul's day; only he who then restrained this anarchy continued to do so until he was taken out of the way. And then the lawless one was revealed (2 Thess 2:7-8). This, of course, took place at the Jerusalem Temple within about 10 years of Paul's writing.
The Thessalonian congregation actually knew personally who was at that time restraining the son of perdition from taking control of the Temple -- "And you know what restrains him now" (2 Thess 2:6).
So the passage has a fulfillment clearly contemporary with Paul and the 1st century Thessalonians exactly as Paul stated. That 2 Thess 2 passage MUST be past in fulfillment.