Stewart Gilligan Griffin is timeless, but his exact age remains a mystery. It's unclear the exact number of years Stewie has been on this planet. The toddler persona from the animated television show "Family Guy" is immortal. His age is yet to be discovered.
Stewart Gilligan Griffin, the cunning infant prodigy, is keeping his age a secret from the world. Speculation abounds 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 captivate fans with his undisclosed age and perpetually youthful visage.

Stewie Griffin Wikipedia