The oldest geographical division of India is the Peninsula. The Peninsula is located in the southern part of India and is surrounded by the Arabian Sea on the west, the Bay of Bengal on the east, and the Indian Ocean on the south. It is characterized by its distinctive shape, which resembles a triangle.

The Peninsula is considered to be the oldest geographical division of India due to its ancient and stable geological formation. It is made up of ancient rocks that are estimated to be over 3 billion years old. These rocks are primarily composed of granite and gneiss, which are some of the oldest rocks found on Earth.

The Peninsula has a diverse topography, with the Western Ghats running parallel to the western coast and the Eastern Ghats running parallel to the eastern coast. These mountain ranges are also considered to be some of the oldest in the world.

The Peninsula is home to several major rivers, including the Godavari, Krishna, and Kaveri, which have played a significant role in shaping the region's landscape over millions of years. The rivers have formed fertile plains and plateaus, making the Peninsula an agriculturally rich region.

The Peninsula also has a rich cultural and historical significance. It is home to some of the oldest civilizations in India, including the Indus Valley Civilization and the Dravidian civilization. The region has a long history of trade and cultural exchange with various civilizations, including the Mesopotamians, Greeks, Romans, and Arabs.

In conclusion, the Peninsula is the oldest geographical division of India due to its ancient and stable geological formation, dating back over 3 billion years. It has a diverse topography, rich in natural resources, and has played a significant role in shaping India's history and culture.