Answer:
My life can be measured in hours, I serve by being devoured. Thin, I am quick. Fat, I am slow. Wind is my foe.
Whilst I was engaged in sitting. I spied the dead carrying the living
I am free for the taking. Through all of your life, though given but once at birth. I am less than nothing in weight, but will fell the strongest of you if held.
What goes through the door without pinching itself? What sits on the stove without burning itself? What sits on the table and is not ashamed?
I am the outstretched fingers that seize and hold the wind. Wisdom flows from me in other hands. Upon me are sweet dreams dreamt, my merest touch brings laughter.
The more of me you take, the more I appear behind you. What am I?