Hi Todd,
I am saying that time is relative based upon several factors (including the perspective of the viewer). The speed of light is considered a universal constant; yet, speed itself is distance divided by time (e.g., meters/second, miles/hour, etc.).
The universe is expanding. This is one reason for the theory of the "big bang." If it is expanding in a roughly uniform direction at a high rate of speed, then it had to have come from a singular point in space.
Consider the various perspectives of those who would have witnessed such an event. You have the perspective from the singular point in space of the "beginning." You have the perspective inside of the expansion of the space (what physicists call the "known universe"). Yet, there is also the perspective of the outside looking in.
Since time is relative, then time will have passed differently based upon the point of perspective. What seems to be a moment from one perspective might be great amount of time from the opposite perspective. Time from the vantage point of the Earth is very different from the perspective outside of the known universe looking in.
This is even more complicated by what we know of the things like escape velocity or how space (and the light in it) "bends" according to gravity influenced by density.
Now, we know what "escape velocity" is. On the Earth, escape velocity is measured at approximately 11.2 km/s (kilometers per second) or roughly 7 miles per second. This is the velocity necessary for something to escape Earth's gravity.
The escape velocity of a black hole -- a star that has collapsed under its own dense mass -- is higher than the very speed of light itself. In other words, light itself cannot escape such a mass.
Now, if light itself cannot escape the velocity of a single star that has collapsed under its own mass, what do you think the "escape velocity" of the mass of the entire known universe must have been? After all, the "big bang" postulates that all mass of the known universe was once together in one massively dense singularity.
If the composition of light cannot escape a black hole -- a single collapsed star -- then how fast must it travel to escape the collective mass of the entire known universe?
If you've watched or read science fiction, then you've undoubtedly seen elements of the variation of time passage as it approaches things like a black hole or other massively dense singularities. Time passes by at different rates relative to the person depending upon their proximity to such a singularity.
In terms of Biblical truth, eternity is a completely different realm where time is viewed differently. After all, a "day with the Lord is as a thousand years and a thousand years is as a day." God knew us before we were born. We are seated with him in heavenly realms. The Lord caught John up and showed him things that would take place long after he breathed his last breath and when his body turned back into dust.
In other words, I am presenting two different things to consider when considering the age of the Earth and, more importantly, the age (and radius) of the universe. One is the relativity of time as understood through perspective. The other is the consideration of the speed of light (and hence time and distance) in regard to the mass of the known universe at the point of creation.
There is, of course, other thoughts to consider. When the Lord created the universe, he could have easily created it in a moment of which the universe and its distance was already predetermined. In other words, light from the most distant stars would have already reached the Earth in that moment of creation.
I hope that this clarifies what I meant.