Universe - The Universe is commonly defined as the totality of existence, including planets, stars, galaxies, the contents of intergalactic space, and all matter and energy. Definitions and usage vary and similar terms include the cosmos, the world and nature.
The age of universe is 14-18 billion years.
Hubble Time -
The inverse of the Hubble constant H has the units of time because the Hubble law is
Thus, the Hubble time T is just the inverse of the Hubble Constant:
The physical interpretation of the Hubble time is that it gives the time for the Universe to run backwards to the Big Bang if the expansion rate (the Hubble "constant") were constant. Thus, it is a measure of the age of the Universe. The Hubble "constant" actually isn't constant, so the Hubble time is really only a rough estimate of the age of the Universe.
Reasonable assumptions for the value of the Hubble constant and the geometry of the Universe typically yield ages of 10-20 billion years for the age of the Universe. For example, H near 50 km/s/Mpc gives a larger value for the age of the Universe (around 16 thousand million years), while a larger value of 80 km/s/Mpc gives a lower value for the age (around 10 thousand million years). Therefore, we shall take this information, and additional information from other methods to estimate the age of the Universe that we have not discussed, to indicate an age of approximately 15 billion years for the Universe.
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