If you believe what Chuck Missler says about Luke 21, that it is a "different briefing" than Matthew 24 and Mark 13, then please take a few minutes and watch this video.
Matthew 1:17—So all the generations from (the generation of) Abraham to (the generation of) David [are] fourteen generations; and from (the generation of) David until the (generation of the) carrying away into Babylon [are] fourteen generations; and from the (generation of the) carrying away unto Babylon unto (the generation of) Christ [are] fourteen generations. Starting with King David they were all periods of 70 yrs (70 yrs x 7 Weeks of Feast).