What Am I Riddles

Question: I am a digit, but two of the ten.
Two of me make a promise.

What am I?

Question: Look at me I want to play.
I'll move like you in every way.
Be tricky, but the result is always a draw.
Why? Because I'm an expert at response and call.

What am I?

Question: The more of me you have, the longer your life.
The more of me you have, the less you have left.

What am I?

Question: With one you can't count past six,
nor can the gap between v and x be fixed.
You can read all of these lines,
but can't say what solves me.

What am I?

Question: I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter.

What am I?