When Starster was originally released, its unlock level was 50. After the Circus content was released, it's unlock level was raised to 60, as that became the new maximum level in the game.
Gameloft includes a brief description of Starster on their Monster Life mini site:
|“||Most Tamanos want to grow up to be stars, but Starster was born one! When she's not dazzling her friends with her brilliant personality and sharp wit, you can find her studying astronomy in Numa's library. She hopes to be an astronaut one day so she can meet other stars like her!||”|