Pretty cool. That looks a whole lot like artificial sinew, which would date it to modern times. Hard to say just from a pic, but artificial sinew has a more waxy feel than real sinew. Is it just for decoration or does it actually bind the ax head to the handle? I use artificial sinew on different projects, but I would have used rawhide to bind the ax head to the handle on this. That's all I can tell you about it.