What Am I Riddles

Question: Looking at my face, I'm no more than six.
Look at the rest of me and I'm 21.
You'll see my twin and me in Las Vegas.
Say my name and you'd be uttering a threat.

What am I?

Question: I am made throughout the world, I am a masterpiece. And to your ears, I am but a humble feast. I am but a traveler, depicted through paper as a start, I can even be made through the work of your heart. What am I?

Question: I have no heart Yet I can live Even if I have fallen Fires are my enemy You are my enemy

Question: The more i am present, the less you can see me. Who am i?

Question: I sizzle like bacon, I'm made with an egg.
I have plenty of backbone, but not a good leg.
I peel layers like an onion, but still remain whole.
I can be long like a flagpole, yet I fit in a hole.

What am I?