Even though no one knows how big the universe could be, we can say that it is immensely large, probably infinite, containing space, galaxies, matter and energy.
The most precise investigation of the age of the universe made by scientists at NASA suggests that its age is 13.73 billion years, plus or minus 120 million years.

There are many definitions of the universe, the definition of it as reality is that universe is everything that exists and it is formed by spacetime, energy (matter and momentum) and physical laws.
Some theorists suggest that this is not the only universe and there could exists other parallel universes or multiverses.