Matthew 16:28
Unlike much of what is in the Bible, that verse seems pretty clear.
Unless you look up the words in a dictionary:
"king·dom (kngdm)
n.
1. A political or territorial unit ruled by a sovereign.
2.
a. The eternal spiritual sovereignty of God or Christ.
b. The realm of this sovereignty.
3. A realm or sphere in which one thing is dominant: the kingdom of the imagination.
4. One of the three main divisions (animal, vegetable, and mineral) into which natural organisms and objects are classified.
5. In the Linnaean taxonomic system, the highest taxonomic classification into which organisms are grouped, based on fundamental similarities and common ancestry. The Linnaean system designates five such classifications: animals, plants, fungi, prokaryotes, and protoctists. See Table at taxonomy."
"Second Coming
Christian Theol. the expected return of Christ, at the Last Judgment"
The passages you quoted indicate that Christ's ministry establishes his sovereignty while the second coming refers to his presence during the last judgment.
Choosing a Catholic explanation only because it was the best one in one particular wikipedia article it says:
"The Kingdom of God began with Christ's death and Resurrection and must be further extended by Christians until it has been brought into perfection by Christ at the end of time.[25]"
So the real question is did his followers not taste death until they saw His death?"