Here's why:

* The Universe is constantly evolving: The universe is about 13.8 billion years old. Stars form from clouds of gas and dust called nebulae. These nebulae are constantly being created and destroyed through processes like supernova explosions and galactic collisions.

* Star Formation is an ongoing process: New stars are still being born today, even in our own Milky Way galaxy.

* Different generations of stars: Stars that formed early in the universe were mostly composed of hydrogen and helium. Later generations of stars, including our sun, were enriched with heavier elements created by the fusion processes within earlier stars.

Therefore, the age of stars varies greatly. Some stars are billions of years old, while others are just a few million years old.