King Cid is a fictional character who first appears in the 1996 video game Final Fantasy VII. He is an ancient and powerful sorcerer who has been alive for over 1000 years. In the game, he is a key figure in the quest to save the world from the evil Shinra Corporation. King Cid is also one of the main characters in the spin-off games Dirge of Cerberus: Final Fantasy VII and Crisis Core: Final Fantasy VII.
In Dirge of Cerberus, it is revealed that King Cid was once a member of SOLDIER, an elite military unit of the Shinra Corporation. He left SOLDIER after becoming disillusioned with their methods and became a wanderer. Eventually, he settled down in Midgar and started his own business. It was during this time that he met Hojo, who would later become his nemesis.
King Cid's age is never explicitly stated in any of the games or other media he appears in. However, based on various clues and hints given throughout the series, it can be inferred that he is at least 100 years old (if not older). In Crisis Core: Final Fantasy VII, when Zack asks him how old he is, King Cid replies Old enough to be your grandfather... maybe even great-grandfather. Based on this statement, as well as his appearance (which shows no signs of aging), it can be assumed that King Cid is well over 100 years old.