The most accurate response to why it is hard to find the age of Earth is: Earth's surface is constantly changing.
This refers to the dynamic processes such as erosion, tectonic activity, and sedimentation that can complicate dating geological features and understanding the planet's history. While radiometric dating techniques provide estimates of Earth's age (approximately 4.5 billion years), the changing nature of the Earth's surface can lead to challenges in directly observing and dating geological formations.