Answer:
When young, I am sweet in the sun. When middle-aged, I make you gay. When old, I am valued more than ever.
It holds most knowledge that has ever been said. But is not the brain, is not the head. To feathers and their masters, it's both bane and boon One empty, and one full.
What tree that definitely grows does not have a shadow and does not grow fruit?
I bind it and it walks. I loose it and it stops.
What surrounds the world, yet dwells within a thimble?
They are many and one, they wave and they drum, Used to cover a state, they go with you everywhere.