Answer:
I can run but not walk. Wherever I go thought follows close behind.
I am free the first time and second time but the third time is going to cost you money.
Curtail me thrice I am a youth; behead me once a snake; complete I'm often used in truth when certain steps you'd take.
I start new then become old. Start clean but become dirty. I usually start big then become little. What am I?
Without a bridle or a saddle across a thing I ride a-straddle. And those I ride by help of me though almost blind are made to see.
What is lighter than what it is made of?