Stewie is forever youthful, but his exact age is shrouded in secrecy. It's unknown the specific duration of time Stewie entered existing. The baby persona from the animated television show "Family Guy" is forever young. His age is yet to be determined.
Stewie Griffin, the clever little troublemaker, is hiding his true age from the world. Speculation abounds as to how many years he has been alive. Is he a century old? Or is he fresh to the world? Only Stewie knows! This mysterious character continues to intrigue fans with his undisclosed age and youthful appearance.

Saison 4 des Griffin Wikipédia