from our universe it's PSR B1620−26 b, believed to be about 12.7 billion years old. From our solar system it's Jupiter (4.503 billion years)

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Assuming you meant from our solar system, yeah, the planets were formed when a whirling ring of cosmic debris around the sun condensed into 9 different balls due to gravity. So you expect them to have close age interval. But Jupiter, as you might notice from its mass, is the oldest.

All planets kinda have same age