Many Preterists, as well as many others in other camps, think that the phrase, "last days" means "the final days of the age." This is simply due to a misunderstanding of the terminology.
The phrase, “last/latter days” is the Hebrew expression that means “future.” It is contrasted with “former” or “beginning days.” It doesn’t, therefore, necessarily refer to the final days of the world. For instance, in Hosea 3:5, God promises blessings in the “last days” to Israel if it returns to Him after it is punished, which clearly indicates what God will do in future days as opposed to the judgment they have received for their past and present sins.
Again, in Genesis 49:1, Jacob assembles his sons to tell them what will befall them in the “last days.” These include Simeon and Levi being dispersed in Israel rather than inheriting land like the other tribes (something that happens in Joshua's day), Zebulun’s tribe being situated at the seashore (also in Joshua's day), Issachar becoming a slave to other peoples (days of the judges), and Dan becoming the judge of the other tribes (days of Joshua and Judges), tribal trouble between Gad and other groups (again, Judges). In other words, they all have to do with blessings and judgments that will happen to the tribes in the future. They concern how prosperous or lacking in prosperity in terms of war, food, riches, wisdom that each tribe will be. This is not concerning the end of the world, but instead, the phrase, “the last days” merely means “future days,” or “in the future.”
Again, in Numbers 24:14, the phrase is used to refer to “future days” when Israel’s king will rise up and crush the Moabites, Amalekites, Kenites (Saul and David accomplish this), not “final days” when all nations will be destroyed and replaced with God’s kingdom. Even though one might certainly read this as a microcosmic foreshadowing of that larger event, it is clear that this specifically speaks to David’s cleansing of the land from the oppression of foreign peoples (2 Sam 8). Hence, the term is talking about “future days,” future from Balaam’s perspective, not “final days.”
In Deuteronomy 4:30, the phrase refers to the post-exilic period when Israel will return from the exile and worship YHWH after being punished.
In 8:16, it refers to God’s intent to discipline Israel in the wilderness in order to do good to them in their future lives in the land of Canaan.
In Proverbs 31:25 (English v. 26), the noble woman has prepared her household so well that when she enters the hemerais eschatais “future," she laughs at it instead of being in distress from lack of preparation.
Ecclesiastes 1:11 contrasts those who lived in the past with those who will live “in the last,” referring only to people who live in the future.
In fact, the term “last” itself is often misunderstood as meaning “final.” Instead, it is clear that the term is related more to the idea of “after,” referencing a point in time as a departure for what is to follow. For instance, Moses speaks of Israel’s continued rebellion against God upon “the last of my death” (Deut 31:27) and “the last of my end” (v. 29), which means “after my death,” and “after my end.”
In fact, it is important to note that the LXX translates the Hebrew aher “after” as eschaton “last” and aher yomim “after days” as eschaton hemeron “the last days.” Hence, one encounters passages like Haggai 2:9, where the splendor of Solomon’s temple’s in the past is contrasted with the 2d Temple’s splendor in future days, as well as Isaiah 41:22 that contrasts the former things with latter things (i.e., past things versus future things).
Where aher and eschatos can refer to the uttermost limit of something, like a body of water or the earth, when speaking about days or the outcome of events, it is most often referring to future days from the person’s perspective when referring to days, not some period of time at the end of the world. In fact, only Daniel may evidence this usage, but even the use there may be in dispute, since it is possible to merely translate the phrase there as “future days.”
This is likely what Paul and Peter mean by statements that indicate mockers will come in “the last days.” The phrase likely means “future days,” not “final days,” as we often interpret it. As such, these are not time references other than contrasting what occurred in the past with what will occur in the times to come.
In fact, what both Paul and Peter describe are things that both occurred in their days and continually occurred throughout their future. Mockers still come with their mocking concerning the coming of Christ. People still seek out teachings that tickle their ears and are corrupt. These are not things of the end that occurred in the days of the apostles, but things that occur in latter days, after days, future days as opposed to the days in the past.