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: When you say my name, I am no longer there. What am I?

Question: I am made of scraps and rags, Yet when I am put together, I keep you warm in the winter. What am I?

Question: To many, I am life's source. I am also its most valuable resource. I create and burn my own precious element, and my destruction will be my punishment. What am I?

Question: Turn us on our backs and open up our stomachs You will be the wisest. What am I?