Haydock Commentary:
Ver. 1. Daughters. These had borne equal proportion with the males from the beginning; but here they are particularized, because they were the chief instruments in corrupting the descendants of Seth. (Haydock) — Even the sons of these libidinous people were so effeminate, as to deserve to be called women. (Menochius)
Ver. 2. The sons of God. The descendants of Seth and Enos are here called Sons of God, from their religion and piety: whereas the ungodly race of Cain, who by their carnal affections lay grovelling upon the earth, are called the children of men. The unhappy consequence of the former marrying with the latter, ought to be a warning to Christians to be very circumspect in their marriages; and not to suffer themselves to be determined in choice by their carnal passion, to the prejudice of virtue or religion. (Challoner) — See St. Chrysostom, hom. 22, &c. Some copies of the Septuagint having the angels of God, induced some of the ancients to suppose, that these spiritual beings (to whom, by another mistake, they attributed a sort of aerial bodies) had commerce with women, as the pagans derived their heroes from a mortal and a god. But this notion, which is borrowed from the book of Henoch, is quite exploded. (Calmet) — The distinction of the true Church from the synagogue of satan, here established, has been ever since retained, as heretics are still distinguished from Catholics. (Worthington) (St. Augustine)
Ver. 3. His days shall be, &c. The meaning is, that man’s days, which before the flood were usually 900 years, should now be reduced to 120 years. Or rather, that God would allow men this term of 120 years, for their repentance and conversion, before he would send the deluge. (Challoner) — He spoke therefore to Noe in his 480th year. (St. Augustine) — Those who suppose, that he foretold this event 20 years later, think with St. Jerome, that God retrenched 20 years from the time first assigned for penance. The Spirit of the sovereign Judge was fired with contending; or, as others translate it, with remaining quiet as in a scabbard, and bearing with the repeated crimes of men. He resolved to punish them severely in this world, that he might shew mercy to some of them hereafter. (St. Jerome, 9. Heb.) (Calmet) — If we suppose, that God here threatens to reduce the space of man’s life to 120 years, we must say, at least, that he did it by degrees; for many lived several hundred years, even after the deluge. In the days of Moses, indeed, few exceeded that term. But we think the other interpretation is more literal, and that God bore with mankind the full time which he promised. (Worthington)
Ver. 4. Giants. It is likely the generality of men before the flood were of a gigantic stature, in comparison with what men now are. But these here spoken of, are called giants, as being not only tall in stature, but violent and savage in their dispositions, and mere monsters of cruelty and lust. (Challoner) — Yet we need not imagine, that they were such as the poets describe, tearing up mountains, and hurling them against heaven. Being offspring of men, who had lived hitherto with great temperance, but now gave full scope to their passions, and the love of the fair daughters whom they chose, we need not wonder that they should be amazingly strong and violent. Nephilim, rushing on, as Ag. translates. That there have been giants of an unusual size, all historians testify. Og, Goliah, &c. are mentioned in Scripture, and the sons of Enac are represented as much above the common size, as the Hebrews were greater than grasshoppers, Numbers xiii. 34. If we should suppose they were four or five times our size, would that be more wonderful that they should live nine or ten times as long as we do? See St. Augustine, City of God xv. 9, 23; Calmet’s Dissert. &c. Delrio affirms, that in 1572 he saw at Rouen, a native of Piedmont, above nine feet high. (Haydock) — Of old. The corruption of morals had commenced many ages ago, and some of the sons of Seth had given way to their lusts; so that we are not to suppose, that these giants were all born within a hundred years of the flood, as some might suppose from their being mentioned here, after specifying the age of Noe, chap. v. 31. (Haydock)
. There it gives a lineage of Seth to Noah and these men could very logically be the “sons of God”. Also, end of Ch 4 gives the lineage of Cain.
I don’t think so, the Catholic Church doesn’t teach so.