Leon Morris, in vol. 3, Luke: An Introduction and Commentary, Tyndale New Testament Commentaries , disagrees with the Brooks interpretation. He writes:
Some see a reference to the people then alive and see the fulfilment in the fall of Jerusalem. The context seems against this, unless, with Plummer, we see the fall of Jerusalem as a type of the end (so Fitzmyer). Many think that Jesus was prophesying the end of all things within a few years and that he was mistaken. In view of his explicit disavowal of knowledge of this point (Mark 13:32), this seems most unlikely. Moreover, as many critics have pointed out, it is impossible to hold that Luke who recorded these words understood them to mean this. In the early church it was often held that the generation of Christ’s followers was meant, so that the elect would persist right through to the end. Others see a reference to the Jewish nation (e.g. Ryle). Some have thought that Luke means us to understand the term in the sense ‘mankind’ (Leaney, Harrington). Lenski draws attention to the frequent use of ‘generation’ in the Old Testament to denote a kind of man, especially the evil (e.g. Ps. 12:7), but also the good (e.g. Ps. 14:5). Similarly Ellis points out that in the Qumran scrolls the term ‘last generation’ apparently ‘included several lifetimes’. It seems that it is something like this that Jesus has in mind. This unusual use of generation concentrates on the kind of people that would persist through to the end. The expression ‘means only the last phase in the history of redemption … The public revelation of the kingdom is just around the corner, but its calendar time is left indeterminate’ (Ellis; cf. Schweizer, ‘since Easter all belong to the generation of the eschaton’).
This expression has been interpreted as referring to (1) Jesus’ own generation, (2) the Jewish people, (3) humans in general, (4) the last generation in history, and (5) Luke’s contemporaries. (Compare how the Qumran community wrestled with the identity of the final generation in 1QpHab 2.7; 7.2.7 and how the ‘final generation’ referred to several generations.) Even though every other reference to ‘this generation’ in Luke can include Jesus’ own generation, it is quite unlikely that here Luke understood ‘this generation’ in this manner because that generation had essentially passed from the scene, and the parousia still lay in the future. The fourth interpretation is so bland as to be meaningless. As long as humanity is present when the Son of Man returns, this by definition must be true; for unlike people in the nuclear generation who wonder if humanity may destroy itself in nuclear war, Luke and his contemporaries had no doubt that the return of the Son of Man would take place in the presence of people. The second suggestion fails to take into consideration that the scene of the coming of the Son of Man is not the ‘land’ (Luke 21:23) of Judea but the ‘earth’ and the ‘nations’ (21:25), so that to restrict the audience here simply to the Jewish people would be to lose sight of the cosmic focus of 21:25–36. Furthermore why would Luke or his readers think that the Jewish people might be wiped from the face of the earth? The fifth suggestion is unattractive to many interpreters since it is obviously wrong. The Son of Man did not come in Luke’s generation. However, in the pursuit of Luke’s meaning one cannot rule out this possible interpretation simply because one does not like it. Nevertheless this interpretation would be strange if in his Gospel Luke was combatting a misunderstanding that the parousia already should have taken place. Luke probably would have been hesitant to date the coming of the Son of Man in such a way.
The third suggestion appears to be the best option. Elsewhere in Luke this expression is used to describe sinful humanity unresponsive to God and oblivious to the possibility of immediately encountering him (cf. 12:16–21, 35–40; 17:26–36). ‘This generation,’ which ignored the coming of the kingdom in Jesus’ ministry, continues in its rejection of the gospel message until the very end. Thus ‘this generation’ of 21:32 stands in continuity and solidarity with ‘this generation’ of Jesus’ day.
We’ll finish up with a couple more scholars in part 3.