Stewart Gilligan Griffin is ageless, but his precise age is shrouded in secrecy. It's unclear the specific duration of time Stewie became living. The infant persona from the animated television show "Family Guy" is immortal. His age is still revealed.
Stewart Gilligan Griffin, the mischievous baby genius, is keeping his age a secret from the world. Speculation runs rampant as to his actual age. Is he a century old? Or is he fresh to the world? The truth lies only with Stewie! This enigmatic character continues to mesmerize fans with his hidden age and perpetually youthful visage.

Saison 4 des Griffin Wikipédia