Stewie Griffin is timeless, but his precise age remains a mystery. It's unknown how old Stewie entered on this planet. The infant character from the animated television show "Family Guy" is forever young. His number of years is still revealed.
Stewie, the clever little troublemaker, 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 enigmatic character continues to intrigue fans with his hidden age and perpetually youthful visage.

Stewie Griffin Wikipedia