I find it difficult to comprehend the age of the universe. To overcome this difficulty, I find it helpful to think of time as a varying dimension.
Time I think originates from our sense of passing intervals, which we are forced to notice, because these intervals reappear rather regularly. We derived the idea of time from the most noticeable one, earths revolution, and made it a universal dimension. Are we entirely right?
If we lock the idea of time to the period of revolution of earth, things seem to be becoming easier to follow. When the big bang took place, all its products would have started spinning at an incredible speed.
Billions of such revolutions might have taken place, during which, cooling and solidification into all the matter in the universe took place. And the initial speed gradually reduced to the present, rather stable, level.
So also, with all other objects.
It is then true, the universe is billions of years old, but each year take lesser and lesser time, as we go back in time.