There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
- King James Bible "Authorized Version", Cambridge Edition
Homer is the author of the Iliad and the Odyssey
We have here on Earth what is called mythology, all over there are stories. tales of so called "Gods" Homer was not the only one who wrote about them, I think that there is only one God, but maybe those so called "Gods" were what the Bible talks about, talks very little about, almost nothing.
Even now, after so very many thousands of years humans have not completely forgoten about them, some religions were based on them.
One of the oldest "books" on Earth is the "Epic Of Gilgamesh" it talks mostly about a person that to me seems to have been more or less like Hercules, not quite "God", but not quite human either, more like in-between, but more human and also mortal.
Even the so called "Gods" such as Zeus, Odin and or whatever seem to not have been quite immortal, just very very long lived, How long lived? I don't know, maybe hundreds or thousands of years (?).
As to they or some of them being giants, well all or at least some of them were probably taller than many or most "regular" humans.
Homer in his books writes that Zeus and his family only drank "Nectar" and only ate "Ambrosia" and nothing else and that that allowed them to live much longer than other humans and that they didn't have regular blood in them, but some other kind of blood.
But in the Bible it talks a little about some people that before the "Flood" lived hundreds of years.
Then the Lord said, My Spirit shall not forever dwell and strive with man, for he also is flesh; but his days shall yet be 120 years.
"And Jacob said unto Pharaoh, The days of the years of my pilgrimage are an hundred and thirty years: few and evil have the days of the years of my life been, and have not attained unto the days of the years of the life of my fathers in the days of their pilgrimage."
Isaac lived a hundred and eighty years.
How to live longer?
Have no accidents
Don't get sick
Eat as we should and eat what we should.
Have the proper state of mind.
Don't get injured.