The short answer to this excellent question is: NO, it is not a good translation.
As a linguist who has worked in Bible translation for 40 years, I have had to study this phrase in detail many times.
A longer answer is here:
Who is this generation? Briefly stated, the tradition more or less equates the word genea with English ‘generation’. This may work in a few places, especially when the word occurs in the plural form, but in the phrase “this genea” it is misleading to use “generation.” It does not seem to agree with the meaning of the Greek phrase or the Hebrew behind it, and it does not make good sense in most places where the word occurs in the New Testament. Rather, genea means ‘a class of people bound together through a common origin or with a common bond.’ In certain contexts genea does have the very restricted sense of the English “generation,” but in most contexts it does not have this narrow sense. The English word “generation” has undergone a semantic shift so that the meaning today is very much narrowed down as compared to the Greek genea, the Latin generatio and “generation” in the English language as spoken when the King James translation was first made.
Even the Vulgate translation used four different Latin words to translate genea, one of which is generatio. But the word generatio is used to translate other Greek words as well, for example, Matt 1:1 genesis (GNB: family record) and Luke 22:18 genēma (fruit). In Danish we have the word “generation” as a modern adopted word. It has the same area of meaning as the corresponding English word, but it is never used to translate genea in the New Testament. In English there is evidence that the area of meaning of “generation” has narrowed down considerably since the time of the KJV translation. The evidence is that the word gennēma ‘brood’ in Matt 3:7 is translated by “generation” in KJV as well as the word genos ‘race, people’ in 1 Pet 2:9. The Oxford Universal Dictionary gives the following, now obsolete (latest attested use 1727) sense of “generation”: “class, kind or set of persons.”
The purpose of the above remarks was to show that the meaning of the Greek word genea is not at all equivalent to the modern English word “generation.” We shall now proceed to discuss what genea actually means.
1 The primary sense is ‘descendants, family, clan, that is, a group of people with a common ancestor’ (see for instance: New International Dictionary of New Testament Theology, 2.35).
This primary sense occurs rarely in the New Testament. With the word in singular it occurs in Acts 8:33: “Who can describe his genea? For his life is taken up from the earth.” Both GNB (Good News Bible), JB (Jerusalem Bible) and NIV translate genea here by ‘descendants.’ The word occurs in plural in Matt 1:17 with a closely related sense of ‘succeeding sets of descendants, stages in a genealogy’ and is probably best translated generations: Matt 1:17 “So all the geneai from Abraham to David were fourteen geneai.”
2 The secondary sense is a natural extension of the first sense and can be stated thus: ‘a group of people with a common bond or characteristic; a certain class or type of people’. This sense is common in the New Testament. The Good News Bible (GNB) often translates it simply as “people.” The characteristic feature of the people referred to is in all cases drawn out from the context. I shall go through all New Testament occurrences of genea below (references in parentheses are to parallel passages).
Luke 16:8: “The sons of this world are more shrewd in dealing with their own genea than the sons of light.” The important contextual clue to the characteristic of the group of people referred to is the word “own” which qualifies genea. Therefore, NIV, NEB (New English Bible) and JB have translated it as “dealing with [people of] their own kind.” The sense is “people like themselves in their worldliness” and not as J.B.Phillips puts it: “contemporaries.”
Acts 2:40: “For he [Peter] testified with many other words and exhorted them, saying, “‘Save yourselves from this crooked genea’.” Here the contextual clue is “crooked.” GNB translates it reasonably well as “save yourselves from this wicked people.” The demonstrative “this” is anaphoric, referring back to the preceding context about the people who rejected the Messiah and nailed him to the cross (v. 36). A more meaning-based (idiomatic) translation of this verse might be: “Disassociate yourselves from those wicked people” or “Turn away from that kind of people, and be saved.”
Phil 2:15: “that you may be...without blemish in the midst of a crooked and perverse genea.” The contextual clue to the characteristic feature of the group of people referred to is “crooked and perverse.” GNB translates: “in a world of corrupt and sinful people.” NLT (New Living Translation) has “a dark world full of crooked and perverse people.”
Matt 17:17: (Mark 9:19; Luke 9:41) “O, faithless and perverse genea how long shall I stay with you?” Again the characteristic feature of the people referred to is shown by the qualifiers: faithless and perverse. Many commentators claim that the word genea has a pejorative character. This is reading the meaning of the contexts into the meaning of the word. This is what James Barr called “illegitimate totality transfer” (1961:218). Rather, the word genea in itself is neutral. The pejorative part of the overall meaning is supplied solely by the connotations of the context.
GNB translates this verse as “How unbelieving and wrong you people are.” J.B.Phillips has: “You really are an unbelieving and difficult people.” NLT has “You stubborn, faithless people!” The actual reference is mainly to the disciples.
Matt 12:39: (Mark 8:12; Matt 16:4; Luke 11:29) “Some of the scribes and Pharisees said to him, ‘Teacher, we wish to see a sign from you.’ But he answered them [scribes and Pharisees], ‘An evil and adulterous genea seeks for a sign...’ “ As usual, the characteristics of the people referred to is shown by the qualifiers: “evil and (spiritually) adulterous.” The actual reference is to those scribes and Pharisees who demanded signs but did not want to accept Jesus.
In translating this passage, the GNB deviates from the pattern set by the examples quoted above. It says: “How evil and godless are the people of this day.” Nothing in the Greek text can justify the addition of the words “of this day.” Maybe the GNB translators had not realised at this point that genea is not the same as “generation”? Or maybe they were influenced by Matt 23:36 discussed below? CEV (Contemporary English Version) is better: “You want a sign because you are evil and won't believe!”
Matt 23:36 (Luke 11:50): “Woe to you, scribes and Pharisees, hypocrites! (See v.23,25,27,29) Truly, I say to you, all this will come upon this genea.” Having seen the pattern from the examples above where genea in itself refers to a class or type of people and the qualifying word(s) and the context describe the characteristic feature of the people, it is natural to expect the qualifying word “this” to point to the characteristics of the group of people referred to. The first instance of “this” refers back to the punishment mentioned in verses 33 and 35 (judgment of hell and the blood of all the righteous). It seems most likely that the phrase “this genea” refers back to the group of people he has just been speaking about. Since this is probably a new thought to many people, I shall spell out some of the arguments in more detail.
There are basically two possible interpretations of the meaning of the demonstrative in the phrase “this genea.” (1) Either it refers to the “people living now” in contrast to people living at another time in history or (2) it refers to something mentioned in the preceding linguistic context. Interpretation (1) is very difficult to reconcile with the basic meaning of the phrase tēn genean tautēn and it also does not fit well with the context. First, there is nothing in the context which supports an idea of temporal contrast. Second, nowhere else can the word “this” possibly be understood as meaning “living now.” Third, and most important, in ALL instances of the phrase “this genea,” the demonstrative follows the noun. As mentioned in section 1 of the full article referenced below, this means that the focus is on genea, not on “this.” If the expression had included a contrast between the generation of that time and any other generation, the word houtos should have preceded genea instead of following it. The second interpretation makes much better sense and is in accordance with the meaning attested to the words “this” and genea elsewhere, that is, “this” is a reference to something in the preceding linguistic context, and genea is a certain type of people.
Now let us look at the context of Matt 23:36. The relevant context is 23:1-39. The whole chapter is one long description and denunciation of the practices of certain hypocritical “scribes and Pharisees” and their like. In verse 35 the reference is broadened to similar people in the past who killed the righteous people (with an obvious sting to the self-righteous Pharisees who would soon kill the righteous Jesus). In verse 37 it is broadened to the people of Jerusalem as representing those people who kill the prophets. Upon SUCH PEOPLE (‘this genea’) will come a great punishment (‘all these things’). A possible, more faithful translation of tēn genean tautēn in v. 36 might be “you and people like you.”
Matt 24:34: (Mark 13:30, Luke 21:32) “Truly, I say to you [disciples], this genea will not pass away till all these things take place. Heaven and earth will pass away, but my words will not pass away.” This is one of the most difficult verses to interpret. Some have argued that the phrase “passing away” suggests that a temporal element is present in the sense of genea here. This does not sound convincing. The next verse says that “heaven and earth” will pass away, while “my words” will not pass away, but no one would suggest that “heaven,” “earth” and “my words” thereby acquire a temporal sense. The word “pass away” does not mean ‘to die’ as GNB suggests. The meaning is much broader and there is no restriction that the subject must be animate as there is in the word “to die.” It simply means “come to an end, cease to exist.” The most obvious meaning of the verse is that certain “things” will continue to exist, while other “things” will cease to exist. Heaven and earth will cease to exist (at least in the present form), but both “my words” and “this class of people” will continue to exist in spite of opposition and tribulation.
It has been suggested that the phrase might refer to the Jewish people as a whole. This, too, I find rather unconvincing. Although the other instances of “this genea” do seem to refer to a group of the Jews, namely those who rejected Jesus as Messiah, this does not necessarily mean that “this genea” always has to refer to Jews. One important difference is that where it refers to the Jews who rejected Jesus, the context has very negative and judgmental connotations. But in this context, the connotations are positive. Whatever the reference is, that class of people will endure through tribulations. By parallelism, the phrase is closely connected to “my words” which is also positive and has endurance. Who would ensure that the words of Jesus were kept in existence through difficult times? It seems to me that “this genea” in this verse most naturally refers to the class of Christians keeping the word of God throughout the ages until the end of heaven and earth. This ties in well with the whole discourse of Matt 24 being directed to the disciples in private (v. 3) and the frequent use of the word “elect” to signify an important thematic participant in the discourse (v. 22,24,31).
A longer answer can be found in my article here: https://www.academia.edu/37043228/Generation_is_a_wrong_translation_choice_for_Greek_genea