The correct answer is 13 billion years ago.
The Big Bang theory is the existing cosmological model for the apparent universe from the most primitive known periods via its consequent large scale evolution. The model illustrates that how the expansion of the universe took place from a very high temperature and high-density state and provides a complete illustration for a wide array of processes comprising the existence of cosmic microwave background, light elements, Hubble's law, and large scale structure.
The complete measurements of the rate of expansion of the universe put the Big Bang at approximately 13.8 billion years ago, that is, thus regarded as the age of the universe.