The universe does not have a center but has a beginning in time and the beginning of space.

The distance to that beginning in time is approx 13 billion years. There is no approximation of distance to the beginning because the space is created at that point and continues to be created.

Imagine the Earth being on the surface of a sphere and so asking what is the center of the surface of a sphere? The sphere has a center but on the surface there is no center.

At least this is my understanding of how to approach these kind of questions.