Mat 24:34 Verily I say unto you, This generation shall not pass, till all these things be fulfilled.
this:
G3778
houtos houtoi haute¯ hautai
hoo'-tos, hoo'-toy, how'-tay, how'-tahee
Including the nominative masculine plural (second form), nominative feminine signular (third form), and the nominate feminine plural, (fourth form). From the article G3588 and G846; the he (she or it), that is, this or that (often with the article repeated): - he (it was that), hereof, it, she, such as, the same, these, they, this (man, same, woman), which, who.
The verse equally can be translated as, "Verily I say unto you, THAT generation shall not pass, till all these things be fulfilled."
Many people use "this generation" as supposed proof Jesus meant the one he lived in and was speaking to but that is faulty since the word equally can mean "that" so we would have "that generation".
Since the generation he lived in and was speaking to did not see the sun and moon go dark, stars fall, the sign of the son of man nor saw the son of man coming, nor the angels gathering the elect which would have included the disciples means without a doubt Jesus was speaking of a future generation.
Additionally, you can talk about a future generation and refer to it as "this generation". Example, "The generation of 3000AD will populate other planets. This generation will be known as the Space Generation."
Equally a past generation can be referred to as "that generation".
Another example. A man points to a red Corvette in his garage, "This car is mine." or "That car is mine." Same thing.