If you're familiar with Thor's adventures, you'll know that he's been drinking ale and kicking butt since the Vikings walked the Earth. How then does he remain looking so young? He is a God, but Asgardians aren't actually born immortal. Instead, they feast on the magical Golden Apples of Idunn, a special kind of fruit which grows in Asgard which allows them to live such long lives. This is something that has been plucked straight from actual Norse mythology, and is used as a way of explaining Thor's immortality. The golden apples were actually featured during one of the first movie's feasts, a very clever Easter Egg by Marvel.