It's an innocuous question, harmless and necessary in the same breath. And for most of us, the answer is just as simple. As children, we dream big because everything around us is big. The world is enormous.
Time is never-ending.
And our future stretches out before us like an endless highway on the prairie. But for some, life is not that simple. That means at ten, he will appear to have a forty year old body. If you play out the math, his lifespan, if he is fortunate, will be about twenty years. Most of us, would try to stop time.