Answer:
I am the ultimate killing machine used not once but TWICE I can be made by humans.
Six letters do my name compound; among the aged oft I'm found; The shepherd also by the brook hears me when Leaning on his crook; but in the middle me divide and take the half on either side each backward read a liquor tell ev'ry gay toper knows it well.
As a state in the USA, I am round on both sides and high in the middle. What am I?
I have a brother. However much we run we do not reach each other.
I plow and plow, but never sow. What am I?
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.