Answer:
Always old, sometimes new. Never sad, sometimes blue. Never empty, sometimes full. Never pushes, always pulls.
It is a part of us, and then replaced. It escapes out bodies, to a better place. The world becomes its sizeable home. Its passions unrestraint, the planet it roams.
What is the freedom of birds and the pen of old men?
I sleep by day, I fly by night. I have no feathers to aid my flight.
The more of them you take, the more you leave behind. What are they?
People take me on walks and I run and have fun. What am I?