Re: How old is Thor?
Honestly, even in the comics, the Asgardians aren't "immortal" in the sense of *never* aging. They just age so slowly that it is, by and large, not an issue.
In the movies? Somewhere right around a thousand years old, it seems. Loki was obviously a newborn right at the end of the war with the Jotuns, and presumably Thor was roughly the same or slightly older. Its anybody's guess on how old Odin and his peers are, though.