At the beginning of Chapter 27, Jesus asked the disciples “What will ye that I shall give unto you?” The answer was that they wanted to know the church’s name.
At the beginning of Chapter 28, Jesus asks a similar question: “What is it that ye desire of me, after that I am gone to the Father?” Although the questions were similar, they appear to differ in whom the question was addressed. In Chapter 27, the address appears to be to the twelve. In these verses, the question is to each disciple individually.
Nine of the twelve want nothing more than the reward of the just. After the “age of man,” or until they die, they will continue to serve the Lord. At that time, they simply want to go to their reward. The difference is perhaps that they would “speedily come unto [the] kingdom,” but the destination is the same as awaits any faithful member.
Jesus blesses them for their desire, and declares that after they live to the “age of man,” here declared to be “seventy and two years,” they would come to his kingdom. Even though this is a specific number, it is probably not meant to be specific. The fact that it contains a multiple of 7 indicates a completeness, thus the “age of man.” The “and two years” likely meant that they would live long— longer that just the normal “age of man.”