system
Given the following post, respond as if you're commenting on Reddit:
human
We say the universe is roughly 13,75 * 10^9 years old. Given that time is relative, from what perspective is this measured?

Edit: After reading a bit about cosmic time I think Coin-coin answered my question in the point I was looking for. Thank all you guys for your contribution, didn't expect that much feedback.
gpt
It's what we call **cosmic time**.

In our model, the Universe is homogenous and isotropic. So there is a special frame: the one in which the Universe is isotropic. If you move in one direction in this frame, you will notice that the Universe doesn't look the same in your direction of movement as in the other directions.

The reference time is the time measured in this special frame.