How Long Is A Generation In The Bible

It is not mentioned in the Bible how long a generation is.

"Truly, I tell you, this generation will certainly not pass away until all these things have happened. Heaven and earth will pass away, but my words will never pass away." - Matthew 24:34-35

It can be conjectured from this passage that generation means people living in this present age, the age between creation and Christ's second coming. The exact date of the second coming of Christ has yet to be discovered, so the present age is an indefinite period of time.