Stewie is eternally young, but his exact age remains a mystery. It's unclear the specific duration of time Stewie has been living. The baby character from the animated television show "Family Guy" is forever young. His age is yet revealed.
Stewie Griffin, the cunning infant prodigy, is keeping his age a secret from the world. Speculation runs rampant as to how many years he has been alive. Is he a century old? Or is he a newcomer? The truth lies only with Stewie! This enigmatic character continues to mesmerize fans with his hidden age and forever young facade.

List of Family Guy cast members Wikipedia