Interestingly, such beings were never referred to as "Gods' by the ancient civilizations.
The Egyptians called them "The Watchers"
The Akkadian; "Ilu" or "lofty ones" (precursor to the Hebrew 'El')
The Caananites and Pheonicians; Ba'al (or Lords)
And the Sumerians the 'Din.Gir', which translates into "the exalted ones of the rocketships".
Incredibly, the pictographic spelling of Din.Gir resembles a multi-step rocketship:
And the Egyptians illustrate such a vehicle in the pharoahs "ascent to the heaven"
Author Zecharia Sitchin explains an interesting phenomenon for their seemingly "immortal" lifespans: their life cycle is based off of the solar orbit of their home planet "Nibiru" which became stuck around our Sun's orbit in an ancient celestrial collision with a planet named "Tiamat" (which used to be located where the asteroid belt now is). Nibiru orbits once every 3600 years and so a humanoid living on that planet would live upwards of 300,000 years.
There is also endless ancient literature describing their life-extending food and drink, so it seems they had such technology to extend their physical lives. A hybrid like those depicted in the bible would certainly live longer than average people but were not immortal (except the ones who were taken to "heaven" and partook of the tree of Life and became immortal)