That's just it. The laws of physics, at least as far as we understand them, absolutely preclude changing our position in any way that would reveal anything outside our observable universe. Lifespans don't come into it at all. If you lived forever traveling at the speed of light, you would never achieve that change of position.

The cosmic background is the leftover "noise" of the big bang, and we observe it roughly uniformly in every single direction. So where did the big bang occur? Everywhere. Everything that exists is precisely at the center of the universe, right where the big bang happened.

It's all about the concept of spacetime. Spacetime isn't space and time considered together, it's a singular thing that operates by rules that we are ill equiped to comprehend intuitively.