I believe that in Matt 16, Jesus is emphasizing the imminence of the kingdom, which begins forthcoming roughly at the time of the resurrection. Thus, when Jesus says the kingdom will be coming during the time his disciples are still alive, he is correct: this is indeed the time period when the kingdom begins coming; it is the time period when the kingdom is imminent. Conversely, in Matt 24 and Luke 21, Jesus is more emphasizing the arrival of the kingdom, an event which occurs much later, at the conclusion of the period of imminence. This arrival of the kingdom is the event Christians are generally thinking of when they say "the second coming of Christ," and this does not occur during the time when the disciples of Jesus are alive. We can ascertain this by the prophetic signs we are told to look for in Matt 24 and Luke 21.

thoughts?