The return of Jesus with the kingdom Jesus is talking about is the new birth and the church that occurred and started at Pentecost.

Matt 16:28 Truly I say to you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.

Jesus did indeed come in his Kingdom during the lifetime of most of those who heard him on that day. The Kingdom of God is in one sense the kingship of God in any one individual’s life. It will also be revealed at the end of time when the final Kingdom of God will be the eternal city”heaven. All this is true, but in the context of Matthew 16:28, Jesus is talking about the kingdom in the sense he most commonly uses it in the gospels. One aspect of the kingdom of God is the church of Christ. The church is the kingdom. In fact, Jesus had just finished making that point in Matthew 16:17-19 where Jesus clearly equates the church with the Kingdom of Heaven and the church began at Pentecost 50 days after the
resurrection.

This fulfillment is found in Acts chapter two. Many prophecies, both in the Old Testament and the New Testament point to the coming of the Kingdom in a new and unique way on the Day of Pentecost. For example, one could look at Isaiah 2:2-4. Daniel 2:44,45, Matthew 3:2,
Luke 24:45-47, Matthew 16:18-20 and Matt 16:28 all point to the events of the pouring out of the Spirit, the first public gospel sermon and the first conversions to Christ which all occurred on the Day of Pentecost, as recorded in Acts chapter 2