As we all already know from Einstein theory of relativity, time, is relative to gravity and speed of the observer. An observer which moves at a faster speed experiences time which is slower than another observer which moves at a slower speed. An observer which on a planet with higher gravity experiences time which is slower than an observer which on a planet with a lower gravity.
In the big bang theory, the universe started off at a singularity point which have near infinity mass, with near zero volume, leading to a near infinity gravity. If there is an observer during the big bang, and the observer is within at the point which have the highest gravity, the observer will observe that it tooks longer for the big bang to happen and expand to bunch of galaxies than an observer who are outside the singularity's gravitational field, whom might observe the big bang happened and expanded to bunch of galaxies in just a few seconds.
We creatures on earth always uses our time scale to measure the age of universe. However, the universe is expanding from a state of high gravity, and each galaxy moves at different speeds and have different gravity, and even earth was rotating at different speed during its early birth, leading to inconsistent measurement of time across this period from big bang to today.
Or am I missing something?