'This generation'
'This generation will not pass away' — the generation then alive (read with the fall of Jerusalem), the generation of the end, or the race of Israel (reading genea as stock); the timetable is read preterist, futurist, and between.
Matthew 24:32-35
32“Now from the fig tree learn this parable. When its branch has now become tender, and produces its leaves, you know that the summer is near.
33Even so you also, when you see all these things, know that it is near, even at the doors.
34Most certainly I tell you, this generation will not pass away, until all these things are accomplished.
35Heaven and earth will pass away, but my words will not pass away.
What each tradition says
Rabbinic / Midrashic
The Jewish Encyclopedia holds that entire chapters in Matthew 24–25 came from Essene apocalyptic literature, the crystallized thought of generations of Essenes, and were put into Jesus’ mouth, consciously or unconsciously. Jesus is presented as the acme and highest type of Essenism.
Joseph Jacobs (1854-1916), Kaufmann Kohler (1843-1926), Richard Gottheil (1862-1936) and Samuel Krauss (1866-1948), The Jewish Encyclopedia (New York: Funk & Wagnalls, 1901-1906), s.v. 'Jesus of Nazareth' — section 'In Theology: The Resurrection' (on the apocalyptic chapters)
Patristic
Chrysostom says that when Christ said “This generation,” He was not speaking of the generation then living but of the generation of believers. He explains that Christ distinguishes a generation not by times only but also by the mode of religious service and practice, as when He says, “This is the generation of them that seek the Lord.”
John Chrysostom (c. 349-407), Homilies on the Gospel of St. Matthew, in Nicene and Post-Nicene Fathers, ser. 1, vol. 10 (ed. Philip Schaff; New York: Christian Literature Publishing Co., 1886) — Homily LXXVII, on Matthew 24:33-34
Catholic
Cornelius à Lapide explains “this generation” in two ways. Following Jerome, it means all men or this age lasting until the end of the world, so all these things will occur before the world ends. Origen, Hilary, and Chrysostom take it more narrowly as the generation of Christian believers sprung from Christ, addressed through the Apostles.
Cornelius à Lapide (1567-1637), The Great Commentary of Cornelius à Lapide, vol. 3: S. Matthew's Gospel, Chaps. XXII-XXVIII (trans. Thomas W. Mossman; Edinburgh: John Grant, 5th ed., 1908) — commentary on Matthew 24:34
Orthodox
No sourced position found. Checked John of Damascus's Exact Exposition (NPNF 2-09), Cyril of Jerusalem's Catechetical Lectures (NPNF 2-07), the Synod of Jerusalem (Confession of Dositheus, 1672; archive.org scan) and the Greek exegetical tradition in English (Theophylact has no public-domain translation); no distinct Orthodox statement on 'this generation' beyond Chrysostom, recorded here under patristic.
Reformed / Protestant
Calvin says that though Christ uses a general expression, he does not extend the discourse to all the miseries that would befall the Church. Rather, before one generation was completed, they would learn by experience that his words were true. Within fifty years the city was destroyed and the temple razed.
John Calvin (1509-1564), Commentary on a Harmony of the Evangelists, Matthew, Mark, and Luke, vol. 3 (trans. William Pringle; Edinburgh: Calvin Translation Society, 1846) — harmony of Matthew 24:32-35
Evangelical
Ryle teaches that these verses mean the Jews will always remain a separate people until Christ returns to this earth. He cites our Lord's words that this generation shall not pass away till all these things be fulfilled, and calls the continued existence of the Jews as a distinct nation an undeniably great miracle.
J. C. Ryle (1816-1900), Expository Thoughts on the Gospels: St. Matthew (New York: Robert Carter, 1860; CCEL text) — note on Matthew 24:29-35