Answer:
When young I am sweet in the sun. When middle-aged I make you gay. When old I am valued more than ever.
The Titanic is still here.
While you were folding a letter you got me. Usually you will do whatever it takes to avoid me but now you can't help but find me.
I am all around, yet to me you are half blind. Sunlight makes me invisible and difficult to find. What am I?
What do you get when you cross a cow with a trampoline?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.