These are generally taken as meaning 120 years before the Flood.
But this mistake has been made by not observing that the word for "men"
in Gen. 6:1, 2 is in the singular number with the definite article, as
v. 3 "man", and means THE MAN ADAM. The word "also" clearly refers to him. It has no meaning if "men" be read, in the plural. It means, and can mean, only that Adam himself, "also", as well as the rest of mankind,. (*1) If "men" be the meaning, then it may be well asked, who are the others indicated by the word "also"?
In Gen. 2:17, the Lord God had declared that Adam should die. Here, in Gen. 6, it was made more clear that though he had lived 810 years he should surely die; and that his breath, or spirit of life from God should not for ever remain in him. See the notes on Gen. 6.
This fixes the chronology of v. 3, and shows that long before that time, A.M. 810, and even before Enoch, this irruption of fallen angels had taken place. This was the cause of all the "ungodliness" against which the prophecy of Enoch was directed in Jude 14, and which ultimately brought on the fulfillment of his prophecy in the Judgment of the Flood. See Ap. 23 and 25.