What is the oldest planet in the milky way?

Answer 1

All the planets in the solar system are approximately the same age. Extrasolar planets are all approximately the same age as the star they orbit.

Population II (low metallicity) stars are the oldest stars, but they're unlikely to have planets.

Answer 2

The Milky Way by a long way. The Milky Way is about 13.2 billion years old, whereas the Solar System is a mere 4.6 billion years old.

Answer 3

The sun and solar system are a part of the Milky Way. The earth is on average approx 93 million miles from the Sun.