The Preterist view is the most obviously wrong, in saying Jesus must have meant the people currently listening to him, they ignore the entire context in which that quote is made.
What I want to discus here is the disagreement among Futurists about whether or not it's valid to see this statement as being about modern Israel.
Throughout history Christians have wanted to believe they are living in the last generation. Those of us living post 1948 feel the main thing that makes our belief the End Times will happen soon more legit is that for most of that history the lack of a nation of Israel in the Holy Land forced Bible Prophecy believers to allegorize everything to make it fit their own time. The Temple is clearly in view in Matthew 24, 2 Thessalonians 2 and Revelation 11.
But none of that makes Israel's founding in 1948 a specific fulfillment of Prophecy. And I agree with the critics of Dispensationalism and Zionisism that the major Bible Prophecies we keep trying to make sound like they're about 1948 are clearly in their Biblical Context about Israelites returning in Belief, and from a Christian POV modern Israel is still in Unbeleif. Those Prophecies are really mainly about either stuff that happens after Armageddon and/or during the Millennium, or the descent of New Jerusalem.
As for Matthew 24, the debate is if the "This Generation" just refers to the ones who see the Signs Jesus had been describing? That seems like the plainest reading, but the Mystery is the Parable of The Fig Tree bares investigating. Matthew 24:32-34
"Now learn a parable of the fig tree; When his branch is yet tender, and putteth forth leaves, ye know that summer is nigh: So likewise ye, when ye shall see all these things, know that it is near, even at the doors. Verily I say unto you, This generation shall not pass, till all these things be fulfilled."Why see the blossoming of this Fig Tree as about Israel?
First there was a curious incident involving a real live Fig Tree earlier in Chapter 21 after Jesus first arrived in Jerusalem for this Passover season. In which Jesus curses a Fig Tree to never bear fruit again, and then it withers and dies. At face value this story interprets itself as being just a demonstration of the power of Faith. But why demonstrate it in such an odd way? Why not demonstrate it by giving life rather then taking it?
Commentators of Mathew's Gospel like Chuck Missler like to view Matthew 13 as when Israel's leadership rejects Jesus as Messiah. If the Fig Tree is in some way a symbol of Israel, Jesus unstated intent may have been for his disciples to realize it's up to them to use the power of their Faith to restore life the Fig Tree that Jesus just withered.
Is there a basis in the Hebrew Scriptures for using the Fig Tree symbolically in such a way?
The first reference in The Bible to a fig trees is in Deuteronomy, that passage like many others is just listing them among various trees.
Judges 9:10-11 uses the Fig Tree as a symbol of Gideon, symbols of national leaders often becomes symbols of the nation.
1 Kings 4:25 describes the nation's peace and prosperity by saying "And Judah and Israel dwelt safely, every man under his vine and under his fig tree, from Dan even to Beersheba, all the days of Solomon." The Fig Tree is affiliated with Israel's prosperity. 2 Kings 18:41 repeats this imagery in the days of Hezekiah, the same situation is again repeated in Isaiah 36-39. And it's used again in Jeremiah 5:17. Later Jeremiah 8:13 says "I will surely consume them, saith the LORD: there shall be no grapes on the vine, nor figs on the fig tree, and the leaf shall fade; and the things that I have given them shall pass away from them."
So all this together makes a re-blooming of a Fig Tree a good symbol for Israel's restoration.
Now to show this interpretation is not purely the result of Darby and other Nineteenth Century Dispensationalists. The apocryphal Apocalypse of Peter which was probably written in the Second Century and was considered canon by many early Christians. Clearly states the Olive Tree is Israel. That writer's agenda in that identification may have been different from anyone today. But the point is it existed.
You might object "Even so, it's about Spiritual restoration not nationally in unbelief". That is true, but the two are linked. Israel's Spiritual Blindness discussed in Romans 9-11 did not fully overtake them over night. It was there from the Birth of The Church, but still the Early Church was mostly Jewish when it started, and in the region remained predominately Jewish until well after the Bar-Kochba revolt.
After Suileman began rebuilding the Wall of Jerusalem from 1534-1541, Zionisim was born in 1561 thanks to Joseph Nasi. And not long after in the wake of the Reformation, especially in the English Speaking world, Christian Zionism is born thanks to men like Thomas Brightman.
Likewise since 1948 Messianic Jews have gown in number greatly. I'm a Dispensationalsit sort of but not a strict one like Pre-Tribers are.
However I will say the fact that it's first and foremost Spiritual means it may be an error to link it to some easily definable Geo-Political calendar date like 1948, or retaking Jerusalem in 1967, or even the yet Future rebuilding of The Temple. It may be referring to the Spiritual Blindness being significantly lifted when the Abomination of Desolation happens. In which case a maximum number for a Generation is not needed.
But I refute the usual argument against Date-Setting here.
What number should be a Biblical Generation?
Hal Lindsay popularized 40 based on the wondering in The Wilderness. F. Kenton Beshore has suggested 70-80 based on Psalm 90:10. We could also use 120 based on Genesis 6, as well as that being about roughly the Maximum people can live to today, and it's how long Moses lived, and about the length of the combined reigns of Saul, David and Solomon. But both Moses siblings were older then him and died earlier the same year. And Jehoiada lived to 130.
There are also dates older then 1948 one could choose if they wanted to. 1897 is considered the Birth of the modern Zionist movement. 120 years from that is 2017, 2017 is popular in some currently trendy Speculation based on a flawed understanding of Revelation 12 which I've addressed before and am highly skeptical of.
1904 was an important year for reasons having to do with William Hechler's efforts and that being the beginning of a major wave of Jewish immigration to the region. 120 years from that is 2024.
In 1909 the city of Tel-Aviv the secular Capital of Modern Israel (or at-least the city the international community recognizes as it's capital) was founded by the ruins of Jaffa the ancient port city of Dan. 120 years from that is 2029.
The Balfour Declaration was in 1917, 120 years from then would be 2037.
1933 was the controversial transfer agreement, 120 years from that would be 2053.
1948+40 was 1988 which notoriously didn't happen. The 70-80 theory gives about 2018-2028 which lines up interestingly with some earlier numbers. 120 years from 1948 would be 2068.
1967 Israel recaptures Jerusalem, the Jewish construction in the Old City was officially allowed around Passover of 1969. Adding 40 years was 2007-2009 which was nothing. Adding 70-80 gets 2037/9-2047/9. Adding 120 years gets 2087-2089.
So it'll be interesting to see how those possible dates line up with other speculative calculations.