Stewart Gilligan Griffin is eternally young, but his exact age remains a mystery. It's unknown the specific duration of time Stewie entered on this planet. The toddler character from the animated television show "Family Guy" is forever young. His number of years is still discovered.
Stewart Gilligan Griffin, the clever little troublemaker, is impossible to determine from the world. Speculation is rampant as to how many years he has been alive. Is he ancient beyond measure? Or is he a newcomer? The truth lies only with Stewie! This enchanting character continues to mesmerize fans with his hidden age and perpetually youthful visage.

Griffin family Wikipedia