Given our knowledge and the standard cosmological model, we estimate that the age of the universe is about 13.7 billion years old.
How much sense does it make to talk about the age of the universe as a whole?
We can observe time dilation so we know time passes differently for observers moving at different speeds (special relativistic time dilation) or located at different distances from centres of strong gravitational fields (as explained by general relativity). Is the estimated age of the universe a property of the universe or of us as its observers?
Would a different observer perceive the age of the universe to be different? Do different parts of the universe have different ages? Do the principles of special relativity even apply when thinking on a universal scale?