(Heb 1:2) but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom also he made the universe.
(1 Cor 10:11) These things happened to them as examples and were written down as warnings for us, on whom the culmination of the ages has come.
Henry Alford had the following to say about Paul's words at 1 Thessalonians 4:17 :
"Then, beyond question, he himself expected to be alive, together with the majority of those to whom he was writing, at the Lord's coming. For we cannot for a moment accept the evasion of Theodoret and the majority of ancient commentators (viz. that the apostle does not speak of himself personally, but of those who should be living at the period), but we must take the words in their only plain grammatical meaning, that 'we which are alive and remain' are a class distinguished from 'they that sleep' by being yet in the flesh when Christ comes, in which class by prefixing 'we' he includes his readers and himself. That this was his expectation we know from other passages, especially from 2 Cor. 5." (Alford's Greek Testament, Vol.III, in loc).
Paul certainly thought that he was living in the last days because he thought that he would remain alive at the rapture. Of course the Christians believed that they were living in the "last days". They knew that after they would be caught up in the air that the remaining prophetic events would begin to take place. First there would be the "great tribulation" and then the general resurrection:
"No man can come to me, except the Father which hath sent me draw him: and I will raise him up at the last day" (Jn.6:44).
"Martha saith unto him, I know that he shall rise again in the resurrection at the last day" (Jn.11:24).
Since you believe that this resurrection has already taken place then tell us when it happened.