With the determination of the age of the universe why do astronomers seems to forget the NON-visible part of the universe?

Since they used the Hubble Constant to measure the expanding speed of the universe, which is now said to believed to be at 70km/s per parsec, roughly? Anyway, by calculating back they come to conclusion that the universe must be about 13,6 billion years old. But what eludes me is they don t take into account ALL... show more Since they used the Hubble Constant to measure the expanding speed of the universe, which is now said to believed to be at 70km/s per parsec, roughly? Anyway, by calculating back they come to conclusion that the universe must be about 13,6 billion years old. But what eludes me is they don t take into account ALL the space that is beyond the horizon. Just imagine, that horizon is nothing else but an edge where the cumulative expansion of space is exceeding the speed of light, but does not mark the spot the universe ends. I don t believe the universe is just 13.6 billion years old. I think it s MUCH older.
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