Now you and I know that generation does NOT usually refer to overlapping lives (just open a dictionary) - but is there something I am missing here? Did they expand on where they got this reasoning from or is this one sentence it?
Any basis whatsoever for that statement?
Thus the words of the Lord here simply asserted that within thirty or forty years all he had been particularly detailing would be fulfilled. Now, the burden of his prophecy had been the destruction of the city and temple, and the signs they were to look for as immediately preceding this great catastrophe.
Arndt and Gingrich note that the term means "literally, those descended from a common ancestor," but "basically, the sum total of those born at the same time, expanded to include all those living at a given time, generation, contemporaries" (W.F. Arndt and F.W. Gingrich, A Greek-English Lexicon of the New Testament and Other Early Christian Literature, Chicago: University of Chicago Press, 1957, p. 153).
Thus, a limit is given within which the prophecies are to be fulfilled. It should be noted that these "tribulations" were not fulfilled in the events of the years 66-73 C.E., the period of the First Jewish-Roman War. Jesus' own statement shows that the culmination of the "tribulation period" was to see the parousia, the second coming of Jesus (Mark 13:26; Matthew 24:3, 30), which certainly did not occur during the war nor subsequently.
Then shall they deliver you up to be afflicted and shall kill you and you shall be hated of all nations for my names sake" (Matthew 24:9).