The truth™ about generations.
"The length of time is indicated by him when he said, "Truly I say to you that this generation will by no means pass away until all these things occur." (Matt. 24:34) The actual meaning of these words is, beyond question, that which takes a "generation" in the ordinary sense, as at Mark 8:12 and Acts 13:36, or for those who are living at the given period."
- Watchtower, July 1, 1951, p. 404
"The word "generation" at Matthew 24:34 is to be viewed in an ordinary sense, as at Acts 13:36 and Mark 8:12. Acts 13:36 speaks of David's very own generation, a literal generation. The generation of persons living in Jesus' time, person who sought a sign, according to Mark 8:12, was a literal generation. That a symbolic application to a "generation" of wicked persons is not meant at Matthew 24:34 is apparent when we read the preceding verse: "Likewise also you, when you see all these things, know that he is near at the doors." It is the generation of persons who "see all these things" to whom Jesus refers in verse 34, irrespective of whether such persons are righteous or wicked. Since Jesus was foretelling conditions prevailing now at the world's time of the end, the generation now living is the one to which he pointed forward in his prophecy of the last days."
- Awake! 1962 September 22 p.27
"Might it be, though, that the sign could occur over the span of many human generations? No. The sign is to occur during one particular generation. The same generation that witnessed the beginning of the sign will also witness its climax in "a tribulation such as has not occurred from the beginning of the creation." Three historians, Matthew, Mark, and Luke, recorded Jesus assurance of this.—Mark 13:19, 30; Matthew 24:13, 21, 22, 34; Luke 21:28, 32."
- Watchtower 1988 October 15 p.4