Hey cloud0729,
Well, since no one else answered, please consider some of what I will present:
Luke 21:32:
With reference to Luke 21:32, I think that Jesus was saying not all of the generation who witnesses those [End Times] events will pass away until the end is finished. I don't believe that Jesus was talking about the generation who was alive when He was.
I have heard a pastor say that we could be that generation who has witnessed some of those fulfilled prophecies, such as the Jewish people reuniting at Israel (after WWII) and then with the Israelis retaking Jerusalem in the Six Day War from the Arabs in 1967.
As for when this generation clock started we do not know (if it has at all; some believe that it started when the Jewish people reunited at Israel, while others believe that it started with the recapture of Jerusalem), and we do not know exactly how long a generation is (a case can be made for up to 100 years). If this interpretation of Scripture is true, then some people who are alive today will see the return of Jesus.
Matthew 16:28 and Mark 9:1:
With reference to the other verses, The Bible Panorama (Chrispin, G. 2005) says that "six days after Jesus teaches that His disciples will see a powerful presentation of God's kingdom before they die, He is transformed before Peter, James, and John in an amazing and glorious way on the mountain" in what is known as the Transfiguration.
Perhaps they believed that Jesus would return in their life-time, but the prophecies regarding His return (such as those in Ezekiel 37-38) had not been fulfilled then...
If you are interested in reading more, then please consider researching on sites like Got Questions Ministries and so on.
Reference:
Chrispin, G. (2005). The Bible Panorama. p. 421. Day One Publications: Reylands Road, Leominster.