MT 24:34 “Truly I say to you, this generation will not pass away until all these things take place.”
And in the next verse, we read:
MT 24:35 “Heaven and earth will pass away, but my words will never pass away.”
Jesus seemed to know that this would be a disputed passage!
Here is a place where “this” means “that”:
Luke 17:34 I tell you, in this [i.e. that] night there will be two in one bed. One will be taken and the other left.
The Tyndale Commentary says we may have a place here where Jesus changes the subject, from addressing the disciples’ first question “when will this happen?”, to address the disciples’ second question: “what will the sign of your coming?”
Yet it may be worth considering that Jesus could have a double fulfillment in mind, that “this generation” does refer to those people now living, and they would see an initial fulfillment of “these things” (which need not include the return of Jesus to reign on earth), and then there would be a later fulfillment, a deeper one, which would be the primary fulfillment.
“Even if ‘generation’ by itself can have a slightly larger semantic range, to make ‘this generation’ refer to all believers in every age, or the generation of believers alive when eschatological events start to happen, is highly artificial. Yet it does not follow that Jesus mistakenly thought the Second Coming would occur within his hearers’ lifetime. If our interpretation of this chapter is right, all that v. 34 demands is that the distress of vv. 4-28, including Jerusalem’s fall, happen within the lifetime of the generation then living. This does not mean that the distress must end within that time but only that ‘all these things’ must happen within it.” (Expositor’s Bible Commentary)
“The ‘all these things,’ of this verse can include no more than the same phrase in the preceding verse and thus cannot include the coming of the Son of Man (so too Blomberg). The phrase refers not only to general marks of the interim period such as tribulation, distress, pseudo-messiahs, and false prophets but specifically, and dramatically, to the desecration of the temple and the destruction of Jerusalem (cf. vv. 15–22). As in the other imminence sayings (cf. 16:28; 10:23; 23:36), all of which like the present saying are prefaced by the emphatic ‘truly I tell you’ formula, the main point is that the fall of Jerusalem was to be experienced by that generation (Kidder), those listening there and then to the teaching of Jesus ‘this generation,’ is used consistently in the Gospel to refer to Jesus’ contemporaries; cf. 11:16; 12:41–42, 45; 23:36). The attempt to explain ‘this generation,’ as the generation alive at the time of the Second Coming or more generally as the human race or people of God goes against the natural meaning of the phrase and makes the words irrelevant both to Jesus’ listeners and to Matthew’s readers. The fact that, as Lövestam has shown, the expression clearly alludes to a sinful generation, one ripe for judgment, fits the fall of Jerusalem (and not merely the end of the age, which is Lövestam’s conclusion).” (Hagner, Donald A., Word Biblical Commentary, Volume 33b: Matthew 14-28, (Dallas, Texas: Word Books, Publisher) 1998)
“The problem is whether Jesus is here referring to the destruction of Jerusalem or to the second coming and end of the world. If to the destruction of Jerusalem, there was a literal fulfillment. In the Old Testament a generation was reckoned as forty years. This is the natural way to take verse 34 as of 33 (Bruce), ‘all things’ meaning the same in both verses.” (A.T. Robertson)