From the context, in verse 24, it is evident that the people who were "standing there" and to whom he was speaking included the twelve disciples. So it isn't a stretch to understand verse 28 to be saying that some of the twelve would still be alive when Jesus returned in the glory of his Father (IE: God) with God's angels, in judgment.
That is not theology or eisegesis, strictly extremely simple exegesis.
So yes, Jesus unambiguously provided the disciples a promise that the arrival of the Kingdom of God and the destruction of Jerusalem, the Temple and the Sinai covenant based Jewish theocracy would occur within the lifetime of some of the twelve.
Jesus made many other similar time promises:
[Matthew 12:41-42 NASB20] (41) "The men of Nineveh will stand up with this generation at the judgment, and will condemn it because they repented at the preaching of Jonah; and behold, [something] greater than Jonah is here. (42) "[The] Queen of [the] South will rise up with this generation at the judgment and will condemn it, because she came from the ends of the earth to hear the wisdom of Solomon; and behold, [something] greater than Solomon is here.
[Matthew 24:34 NASB20] (34) "Truly I say to you, this generation will not pass away until all these things take place.
[Mark 13:30 NASB20] (30) "Truly I say to you, this generation will not pass away until all these things take place.
[Luke 11:29-32, 51 NASB20] (29) Now as the crowds were increasing, He began to say, "This generation is a wicked generation; it demands a sign, and [so] no sign will be given to it except the sign of Jonah. (30) "For just as Jonah became a sign to the Ninevites, so will the Son of Man be to this generation. (31) "The Queen of the South will rise up with the men of this generation at the judgment and condemn them, because she came from the ends of the earth to listen to the wisdom of Solomon; and behold, [something] greater than Solomon is here. (32) "The men of Nineveh will stand up with this generation at the judgment and condemn it, because they repented at the preaching of Jonah; and behold, [something] greater than Jonah is here. ... (51) from the blood of Abel to the blood of Zechariah, who was killed between the altar and the house [of God;] yes, I tell you, it shall be charged against this generation.'
[Luke 17:25 NASB20] (25) "But first He must suffer many things and be rejected by this generation.
[Revelation 3:11 NASB20] (11) 'I am coming quickly; hold firmly to what you have, so that no one will take your crown.
[Revelation 22:7, 20 NASB20] (7) "And behold, I am coming quickly. Blessed is the one who keeps the words of the prophecy of this book." ... (20) He who testifies to these things says, "Yes, I am coming quickly." Amen. Come, Lord Jesus.
[Revelation 2:16 NASB20] (16) 'Therefore repent; or else I am coming to you quickly, and I will wage war against them with the sword of My mouth.
And we see it promised elsewhere:
[Matthew 3:10-12 NKJV] (10) "And even now the ax is laid to the root of the trees. Therefore every tree which does not bear good fruit is cut down and thrown into the fire. (11) "I indeed baptize you with water unto repentance, but He who is coming after me is mightier than I, whose sandals I am not worthy to carry. He will baptize you with the Holy Spirit and fire. (12) "His winnowing fan [is] in His hand, and He will thoroughly clean out His threshing floor, and gather His wheat into the barn; but He will burn up the chaff with unquenchable fire."
The promised destruction of the Temple, Jerusalem and the Jewish theocracy were, in fact, accomplished c. 70 AD/CE in the form of the horrific nightmare seven year war with Rome.