Which of the following statements regarding the age of the universe is true?

The age of the universe is determined through various observational methods, including studying the cosmic microwave background radiation and the movement of galaxies. Current estimates based on these methods indicate that the universe is approximately 13.8 billion years old. This figure is widely accepted within the scientific community and is supported by findings from missions such as the Planck satellite, which provided high-precision measurements of the cosmic microwave background.

The other statements either underestimate or overestimate the age of the universe. For instance, stating that the universe is less than 10 billion years old is not consistent with the wealth of astronomical evidence that points to a much older universe. Similarly, claiming that the universe is over 20 billion years old also lacks support from observational data. Finally, asserting an exact age of 15 billion years does not account for the uncertainty and range of estimates that scientists have established. Hence, the most accurate representation of the current understanding of the universe's age is that it is approximately 13.8 billion years old.