The reason we don't see many "large" elderly people

My sister is six feet tall. One day she asked me why we don't see many large old people walking around.

"Well, I said, it's because large people put more stress on their bodies and die sooner, and also because people shrink with age."

"No, she replied. That is not the reason we don't see them. It's because they hide inside their houses so they don't scare children!"