It is. First of all, it's a branch of Indo-European mythology, as are the Greek, Roman, and Hindu pantheons. So it has existed in some form for thousands of ye

It is. First of all, it's a branch of Indo-European mythology, as are the Greek, Roman, and Hindu pantheons. So it has existed in some form for thousands of years. But "Norse mythology" as we know it was mostly written down in the 13th century - so 700+ years ago.