Answer:
Both old people and owls are said to be possessing this trait
I build up castles. I tear down mountains. I make some men blind. I help others to see.
It is weightless, you can see it. If you put it in a barrel it will make it lighter?
Without this, eating food and Steven Spielberg's career would be very different.
What is that which, though black itself, enlightens the world without burning?
Sometimes I am white, sometimes I am dark. Most people love me. What am I?