I'm tall when I'm young, I'm short when I'm old. What am I?

Why this works

This riddle plays on the physical characteristics of both a candle and a pencil as they are used over time. When a candle is new (young), it is tall, but as it burns down (ages), it becomes shorter. Similarly, a pencil starts off long when it's new but gets shorter as you use it and sharpen it. The clever twist lies in the idea of aging—both items lose height and become "short" as they are utilized!