Human

Stardust thinks it over "This is a famous riddle and the answer is staring me right in the face, Human. Human is my answer. You, humans, start by crawling on our arms and legs as babies then learn to walk on two legs as an adult then when you grow old you require the use of a walking stick. I have seen it as my Lady grew up and when my Lady's father comes to visit."

"Very well reasoned, I did not think you would get it. Had I known the old king uses a cane then I would have asked a different riddle, well I guess I have to wait my turn ." You reply.

"My turn" Replies Stardust "This thing all things devours: Birds, Beasts, Trees, Flowers. Gnaws Iron, Bites Steel Grinds hard Stone to meal, Slays Kings, Ruins Towns and beats high mountains down."