I tend to regard the phrase “this generation” as referring to the people who were alive at the time when Jesus was teaching for this reason. As you know, chapter divisions were not in the original writings and in Luke 20-21, Jesus was teaching publicly at the temple when asked about the signs of the end of the age. In Luke 21:12, Jesus said “but before all these things” (KJV) and then spoke about the persecution and destruction that was to happen in 70
Most scholars equate Matt 24-25, Mark 13 and Luke 21:5-36 beginning in verse 5 as being the same. Luke’s account is the only one that deals with the disciples’ first question, “When will these things happen?” It concerned His prophecy that the Temple would be destroyed.
After opening with a general comment on the End Times, He brought them back to the 1st Century in verses 12-24 before concluding with an End Times summary. Your interpretation of that part of the Luke passage is correct. But notice how He also used the phrase “this generation” in Luke 21:32 within the framework of the End Times.
In Matthew’s account, the phrase “this generation” is only used in speaking of of the End Times. Beginning in Matt. 24:15 Jesus spoke of an Abomination of Desolation yet to come, and in verse 21 said that it would signal the beginning of the Great Tribulation. In verses 29-30 he said that after the Great Tribulation ended, the people of earth would see the sign of the Son of Man in the sky, followed by His 2nd Coming. Then He said that this generation would not pass away until all these things have happened. Matt. 24:34
Here, the phrase “this generation” refers to the generation being born at the time when the End Times signs begin. His point was that all the End Times prophecies will be fulfilled within the lifetimes of the generation being born when they begin.