the old fogies of the Marvel Universe

I was just reading up on the debate regarding Thanos's age, and apparently the thinking is that he's, at the least, 4,000 years old, and at most, possibly about 748,000 years old. Which puts Eros at about the same age as Thanos, and the rest of the Titan-born Eternals somewhere in between. Assuming that the truth is somewhere closer to the higher end, who's older than these guys? Besides the Earth-born Eternals. Or are the Earth Eternals actually younger? I forget. Have the gods of Asgard been around as long? I mean, how old is Thor, anyway? The Greek gods? Who are the real old codgers in the Marvel Universe?

-Justin