Are you sure about that. The Jews in Jesus' day would have compared what jesus was teaching with the OT to see if He was right.
Why has this changed?
In the OT, there are two Hebrew root words that have been translated into English as "generation."
One is speaking of "descendant generations" while the other is referring to an age. When the LXX was being translated into the Greek Language, the Greek word used for H:1755 was "genea." The other "Hebrew word for "Generation," is found in H:8435 a very different Hebrew word.
Genesis 10:32: - Αὗται αἱ φυλαὶ υἱῶν Νῶε κατὰ γενέσεις αὐτῶν, κατὰ τὰ ἔθνη αὐτῶν· ἀπὸ τούτων διεσπάρησαν νῆσοι τῶν ἐθνῶν ἐπὶ τῆς γῆς μετὰ τὸν κατακλυσμόν.
Genesis 10:32: - These were the families of the sons of Noah, according to their generations, in their nations; and from these the nations were divided on the earth after the flood.
Now, the Greek word found in Matt 24:34,
γενεὰ is very different to the Greek word
γενέσεις used in the LXX at Gen 10:32 which is associated with descendant generation, which is how you are wanting to understand
γενεὰ in the Matt 24:34 verse.
Our understand of the language must be drawn from the time it was written, not from our understanding of language usage of today.
Your understanding of the meaning of Matt 24:34 is flawed, and as much as I disagree with Quitethinker, his understanding of an age being referenced by Jesus in the Matt 24:34 verse is in agreement with my understanding. Jesus was referring to the Millennium Age, which is the last age for Mankind in our present state, and many of the things we were told where with reference to the distant future from the time of His first advent.
You cannot just read the NT without having a good understanding of the OT, and neither trumps the other.
Shalom