That's the frustrating thing (well, one of them) about learning physics, science etc - coming up with a question that you know you really should be able to answer. I think the solution is to keep reading. Or ask someone cleverer! Yes :)
So what I am stuck on is this - relativity says that there is no universal measure of time, that it's dependent on relative motion. A photon of light, moving through space at the speed of light, won't experience any time as it moves.
But science has measured the age of the universe to be 13.73 billion years. Given the effect of relativity, would an alien being in another galaxy zooming away from us at some great speed measure the same age for the universe? How does relativity affect the measurement of that age?