Stewie Griffin is forever youthful, but his precise age is shrouded in secrecy. It's unknown how old Stewie became on this planet. The infant persona from the animated television show "Family Guy" is forever young. His number of years is yet discovered.
Stewart Gilligan Griffin, the mischievous baby genius, is keeping his age a secret from the world. Speculation is rampant as to the length of time he has existed. Is he a century old? Or is he a recent arrival? The answer is known only to Stewie! This mysterious character continues to intrigue fans with his hidden age and forever young facade.

Saison 4 des Griffin Wikipédia