THREE RHYMING RIDDLES

1)
Some foolish young who have this
Would sell it to the old;
And the old would gladly buy it,
If indeed it could be sold.

2)
I mock the swiftest bird in flight,
Never stopping - day or night;
By lack of me are dreams unfulfilled,
Yet I'm wasted, lost, and killed.

3)
To change I have power,
On the half or full hour.

Answers:

1. Youth 
2. Time 
3. TV remote control