Verse 34 of Matthew 24 is the time text.
The Greek word “genea” (pronounced ghen-eh-ah') appears thirteen times in Matthew's gospel. Four times it is used to delineate “one set of parents to the next”. Every time the definite article “this” (houtos) is found before “generation”, i.e.“this generation” (houtos genea), in every gospel on the lips of Jesus, in context, clearly covers the same group of people -i.e. “Christ's faithless contemporaries”
So everything before Matthew 24:34 applied to Christ's generation and in fulfillment of Matthew 23:36 Scripturally speaking, there is no other possibility.
Looking at the other generational applications.
Could Jesus have meant that:
a. "all these things"
were to happen to the 20th century
- Impossible: conversation
centers on "these stones"
which were knocked down in 70 AD.
- Impossible Lu.21:23-24
states that subsequent to great
distress, Jews were to be led captive to all nations which
occurred immediately after the 70 AD destruction.
b. "all these things" were to happen to both Christ's
generation and our generation. (dual fulfillment theory)
- Impossible: -these buildings and are already destroyed.
- Impossible -Jews are not
to be led captive into all
nations again at Christ's second coming.
- Impossible -Matt.24:21 precludes dual fulfillment.
This leaves only one scriptural option i.e. that
c. "all these things" were to happen to Christ's generation
I don't believe we can apply things after verse 35 to "this generation". The material is incompatible with just about everything that appears before it.