The age of the universe is about 13.75 billion years. The diameter of the observable universe is estimated at about 28 billion parsecs (93 billion light-years). As a reminder, a light-year is a unit of length equal to just under 10 trillion kilometres (or about 6 trillion miles).
The Observable Universe consists of the galaxies and other matter that we can, in principle, observe from Earth in the present day—because light (or other signals) from those objects has had time to reach the Earth since the beginning of the cosmological expansion.
The word observable used in this sense does not depend on whether modern technology actually permits detection of radiation from an object in this region (or indeed on whether there is any radiation to detect). It simply indicates that it is possible in principle for light or other signals from the object to reach an observer on Earth.
The numbers are pretty hard to comprehend even when you know what each unit represents. To even think of how long 10 trillion kilometers might be, let alone 93 billion times that distance, can cause your brain to hurt. Andrew Z. Colvin has attempted to put some of this incomprehensible size into perspective by starting with our own planet and zooming out from there.
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