This is a question that has been grasping my attention for some time now.
How old is Thor?
We see him in 893 AD in viking-era Scandinavia in the first issue of God of Thunder so that puts him at being at least 1,120 years old. Considering he is visibly an adult during that time and taking into account the general lack of aging seen from 893 to the 21st century it is safe to assume that he could be thousands of years already by the time he was worshiped by the vikings. Its also not out of the realm of possibilities for Thor to be in the millions of years age range though either. I would think Odin has surely been around that long. In the RTK story arc I think, its shown that the forging of Mjolnir by order of Odin was the cause of the extinction of the dinosaurs. We can only really be sure that Thor is at least 2,000 years old in my opinion. I would guess much more though.
Thor is inconsistent years old. So many different writers, so many different stories, so many that conflict with each other. I mean in some stories we have an adult and mature Thor around in ancient Egypt, but some other stories, he is young and brash in 1000 AD. Do you also include Ragnarok cycles? From what I remember the was a Ragnarok around 4000 years ago. Then again the process of creating Mjolnir supposedly killed the dinosaurs as well, 65 million years ago... so... my best answer is Inconsistent. Throw in the whole Ragnorak cycle and mystical/mythological nature of Thor and I reckon anyone (writers included) could make up their own answer (provided its closer to being "old" than "young") and be right, naturally accepting that other people could assert other answers and also be right too.
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