i think it is clock
Analog clock
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?
Look at me. I can bring a smile to your face, A tear to your eye, Or even a thought to your mind. But, I can’t be seen. What am I?