Step 1: Understand the question.
We need the oldest fold mountain system in India.
Step 2: Identify the range.
The Aravalli Range is the oldest fold mountain system in India and one of the oldest in the world.
Step 3: Its features.
It formed over a billion years ago, has worn down due to erosion, and runs from Gujarat through Rajasthan to Delhi. Guru Shikhar is its highest peak.
Step 4: Rule out others.
The Himalayas are young fold mountains. The Satpura is a block mountain. The Western Ghats are escarpments of the Deccan Plateau.
Step 5: Conclude.
The oldest fold mountains are the Aravalli Range.
Answer: Aravalli Range