I am always 1 to 6.
I am always 15 to 20.
I am always 5.
I cant be 21 unless flying

What Am I?

Dice (6 sided)

* I am always 1 to 6: numbers on dice are from 1 to 6.
* I am always 15 to 20: Sum of all the visible sides (1 top and 4 on the sides) always add up to 15 to 20.
* I am always 5: Five sides are visible.
* I cant be 21 unless flying: When we throw the dice, we can see all 6 sides for a small moment which all add up to 21.