Answer:
I have one, you have one. If you remove the first letter, a bit remains. If you remove the second, bit still remains. If you remove the third, it still remains.
I am a box that holds keys without locks, yet they can unlock your soul.
When young, I am sweet in the sun. When middle-aged, I make you gay. When old, I am valued more than ever.
White bird, featherless, flying out of paradise. Flying over sea and land. Dying in my hand.
Both punishment and sweet reward, It will befall both fool and lord. It is a spiritual scoreboard, Your every deed it does record.
Iām grown from darkness but shine with a pale light. Very round I am and always a lady's delight.