Here's an excerpt from David Kroll's When will Christ Return?
Is the coming of Christ on clouds to be taken literally? How is this expression used in scripture? In Isaiah 19:1, in a prophecy concerning Egypt, it is written, “See, the Lord rides on a swift cloud and is coming to Egypt.” In Psalm 18:9, David, in a psalm of praise to God for deliverance from his enemies, writes, “He parted the heavens and came down; dark clouds were under His feet.” In another psalm of praise, David speaks of God in this manner: “He makes the clouds His chariot and rides on the wings of the wind” (Psalm 104:3). Coming in the clouds, riding on the wings of the wind, like many other expressions concerning the activity of God in the scriptures, are simply expressions of God’s magnitude of power and presence as He intervenes in the affairs of men. These are not literal expressions of how God appears.
...Christ uses an object lesson to demonstrate to His disciples that when they see come to pass all the things He had just predicted; the wars, famines, earthquakes, the gospel going to the world, etc., His coming would be at hand. Christ said just as they would know that summer is near when they see leaves come out on a fig tree, so they would know that the end was about to occur when they see all these events taking place. Christ then dates the events He is discussing by saying that the generation He was addressing would not pass until all the things He was speaking of would come to pass. All “these things” included His return (verse 30). What generation is Christ addressing? To what time was He dating these events?
It must be remembered that Christ is addressing His disciples in the Olivet discourse. He is answering their questions about when the temple will be destroyed and His return will take place. In addressing His disciples, He says to them, “Even so, when you see all these things, you know that it is near, right at the door.” Christ then makes the statement about their generation not passing until all these things are fulfilled. The “you” Christ is addressing are his disciples. Christ is not addressing us or anyone else. It must be understood that when we read the Olivet discourse, we are reading a record of Christ addressing His disciples. When Christ tells them “when you see all these things,” He is telling them that it is they who will see all these things, not others living thousands of years into the future.