I'm 20 years old, few years ago i hit the lower back right side ofmy head on a hard poll type surface. i have bump now but doesn't hurt. damage brain?

Doubt: If you had a brain damage then, it would have manifested itself by now. The bump you are feeling is most likely coming from the outer structures - skin, underlying fat tissue, fascia or perhaps, bone, but not the brain. A ct scan of the head or ultrasound might be helpful to figure this out.

You are OK: If there were not effects at the time, over these many years your brain has proven its usual resilience, and has suffered no ill effects. If there is a non-painful bump, you can probably ignore it but if it bothers you and affects things like combing your hair, then see your family doctor for diagnosis.