In Acts 2:15, Peter quotes the prophecy of Joel 2:28f about the last days and emphatically says: “This is that” which was spoken by the prophet Joel.
“This is that” does NOT mean “this is not that!”
Peter not only affirmed the last days had arrived in the first century, he repeated it in Acts 3. He said that all of the prophets from Samuel forward, “foretold these days” (Acts 3:24).
Hebrews 9:26 deals a crippling blow to the idea that the last days are yet future. The writer says Jesus, “has appeared once, at the end of the age to put away sin by the sacrifice of himself.”
The question is at the end of what age did Jesus appear?
He surely did not appear at the end of the Christian age.
Jesus appeared under the Law (Gal 4:4), in the fullness of time. Thus, he appeared in the last days of the age of the Law, the last days of Israel, the last days of the Jewish age.
Paul insisted he was living in the end of the age (1 Cor 10:11 and Heb 1:1).
If the Jewish age was to end and the Christian age has no end, what age was about to end? (Heb 1:1; Js 5:3; 1Pet 1:20; Jude 18; 2Pet 3; 1 Jn 2:18)
What last days were they living in?
Time statements are consistently used, literally through the Bible, but the language of the “Day of the Lord” is consistently metaphorical throughout the Bible. There is not one example of “The Day of the Lord” language, ie: coming on the clouds, with fire, the Shout, The Trumpet, etc ever being fulfilled literally.