In conclusion, those who were standing there would not taste of death before they saw the kingdom of God coming with power, were Peter, John and James and it was fulfilled when the witnessed Jesus' transfiguration into His glorified state, as well as the appearance of Moses and Elijah.
I guess it depends on what the kingdom of God means to you. For me,
I take the kingdom of God as an earthly kingdom that is based on Jerusalem. I used these few OT passages to explain
Zechariah 8 explains
3 “Thus says the Lord: ‘I will return to Zion, And dwell in the midst of Jerusalem. Jerusalem shall be called the City of Truth, The Mountain of the Lord of hosts, The Holy Mountain.’
Later on, in the chapter in Zechariah 8:20-23 New Living Translation (NLT)
20 “This is what the Lord of Heaven’s Armies says: People from nations and cities around the world will travel to Jerusalem. 21 The people of one city will say to the people of another, ‘Come with us to Jerusalem to ask the Lord to bless us. Let’s worship the Lord of Heaven’s Armies. I’m determined to go.’ 22 Many peoples and powerful nations will come to Jerusalem to seek the Lord of Heaven’s Armies and to ask for his blessing. 23 “This is what the Lord of Heaven’s Armies says: In those days ten men from different nations and languages of the world will clutch at the sleeve of one Jew. And they will say, ‘Please let us walk with you, for we have heard that God is with you.’”
A similar prophecy was given in Micah Chapter 4 (NLT)
In the last days, the mountain of the Lord’s house will be the highest of all—the most important place on earth. It will be raised above the other hills, and people from all over the world will stream there to worship.
2 People from many nations will come and say, “Come, let us go up to the mountain of the Lord, to the house of Jacob’s God. There he will teach us his ways, and we will walk in his paths.” For the Lord’s teaching will go out from Zion; his word will go out from Jerusalem.
Finally, the same prophecy was given in the book of Isaiah chapter 2:2
In the last days, the mountain of the Lord’s house will be the highest of all—the most important place on earth. It will be raised above the other hills, and people from all over the world will stream there to worship.
So, based on these accounts, all the Jews are to be saved first, once they accept Jesus has the Messiah, then the Kingdom will be established in Jerusalem and the Jews will then be priests spreading that blessings to all the Gentiles.
That was the original plan and timetable, but alas, the Jews rejected God thrice, they rejected God the Father in the OT, they rejected God the Son in the 4 Gospels, and they rejected God the Holy Spirit in Acts with Stephen stoning. The last sin was deemed unforgivable under the law. Hence the postponement of that plan, to the benefit of all of us Gentiles.