No one knows, except the One who created it. The scientific establishment gives us a few guesses. Several “billions of years”, they assert with great confidence. Their conclusion is based on the “big bang” theory I suppose. That and the fact that they assume that it created itself somehow, since considering that there’s a real Creator isn’t considered kosher in their definition of “science”. So, they had to come up with something.
We seem to have a basic understanding of how light travels, at least currently. Assuming that it also “created itself”, you can feel somewhat confident that light will behave this way forevermore. Light travels currently at the “speed of light”, or does it? That may be true when referenced to it’s point of origin, let’s say a flashlight. Tiny “particles” called “photons” as shed by a heated tungsten filament and shoot out into the air traveling away from the flashlight at a “the speed of light” give or take a little depending.
Now, what if you place two flashlights back to back and turn them on? The “photons” leaving the one flashlight would be moving 2X the “speed of light” from the “photons” leaving the other flashlight facing the opposite direction. So, the “speed of light” is only relative to the object emitting it.
Based on a 6.5 billion year old universe “big bang” creation story or “theory”, you would predict that all objects over 6.5 billions “light years” away would not yet be visible from our vantage point. Their light “photons” would not have reached us yet. Of course that would depend on the location of the “epicenter” of the “big bang”. If it was 5.5 billion light years away, then the light from almost half of the universe hasn’t made it here yet.
Based on a “natural theology”, that is, “nature did it”, you are forced to imbue nature with the powers needed to get the job done. Pushing the event way out somewhere in the far distant past helps to conceal your uncertainties especially when nature is lacking in smarts and isn’t allowed to have any intelligence per se.
The tale of the self-created universe! How did I ever take that stuff seriously? So, how old is the earth anyway? Pretty old is my guess.