No one has mentioned:
Jesus didn’t know as a man, when it was to happen.
So, He would have meant something else by “generation”, that probably made sense to them, but was not what we mean by the term today.
Jesus may have been able to say, that no one knows the day or hour, but our Father in Heaven, that doesn’t negate that Jesus knew it would be within 40 years, besides the Olivet Discourse coincides with Revelation, where you have Jesus using language like
Soon and
Near
Revelation 1:1 The revelation of Jesus Christ, which God gave him to show to his servants what must soon take place; and he made it known by sending his angel to his servant John, 2 who bore witness to the word of God and to the testimony of Jesus Christ, even to all that he saw. 3 Blessed is he who reads aloud the words of the prophecy, and blessed are those who hear, and who keep what is written therein; for the time is near.
If I was an 80 year old man, I could confidently say, I do not know the day or hour of my death, but I know it will be within 40 years and not be contradicting myself, being that the likelihood of me living to 120 years of age is all but nill. When my Grandmother passed, she did not know the day or hour when she was 65, but when she was 86 years old in hospice, she knew the time was near, and soon, in fact, she knew that it would be within a day or two, from her failing health, so much that she would request a priest on call, so she may receive the Viaticum. The priest came by, and she passed on, within a few hours!
So Jesus knew that it would be a generation, He would give a heads up on what would take place, within the generation, and after his assention, He would reveal to St.John that it was soon, and near, as the generation was coming to an end, and His
this generation statement came to pass with the fall of the temple in A.D.70
God bless!