Hi Morocco, You asked about this. Not to say that I am a bible scholar just a simple man. But I believe that Matt. 16:28 is fulfilled in Matt. 17 when some of those present heard Jesus and witnesses him in kingdom glory at his transfiguratiion.
Luke 9:27, Mark 9:1, Matt. 16:28
“I tell you the truth, some who are standing here will not taste death before they see the kingdom of God."
Now in these scriptures Jesus is speaking of the people “standing here” or those listening to him speak. That's pretty hard to subject to a future tense. Perhaps, though, it could be understood in a different light. It said “before they see the kingdom”, maybe that was speaking about seeing it in a vision or having prophetic dreams. Perhaps it meant something other than seeing the kingdom coming to earth.
Matthew 17
The Transfiguration
1 After six days Jesus took with him Peter, James and John the brother of James, and led them up a high mountain by themselves. 2 There he was transfigured before them. His face shone like the sun, and his clothes became as white as the light. 3 Just then there appeared before them Moses and Elijah, talking with Jesus.