Answer:
It doesn't live within a house, nor does it live without. Most will use it when they come in, and again when they go out.
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.
There is a creature of God whose body is hardΝΎ it does not wish to eat unless you strike its head.
What is it that you must give before you can keep it.
Look into my face and I'm everybody. Scratch my back and I'm nobody.
You can always find me in the past. I am created in the present, but the future can not change me. What am I?