Stewie Griffin is ageless, but his precise age is shrouded in secrecy. It's unknown the specific duration of time Stewie entered on this planet. The toddler character from the animated television show "Family Guy" is immortal. His time on Earth is yet to be determined.
Stewie, the cunning infant prodigy, is keeping his age a secret from the world. Speculation is rampant as to how many years he has been alive. Is he a century old? Or is he a recent arrival? The truth lies only with Stewie! This mysterious character continues to mesmerize fans with his undisclosed age and perpetually youthful visage.

List of characters in the Family Guy franchise Wikipedia