There's no such thing as a "galactic year". Here's why:

* Galactic Rotation: Galaxies rotate, but they don't have a fixed period like planets orbiting stars. The time it takes our Milky Way galaxy to complete one rotation is estimated to be around 250 million Earth years.

* Earth's Age: Earth is approximately 4.54 billion years old.

So, while we can calculate the Earth's age in Earth years, we can't express it in "galactic years" because there's no standard definition of a galactic year.