Stewart Gilligan Griffin is forever youthful, but his specific age is shrouded in secrecy. It's unclear how old Stewie became existing. The toddler persona from the animated television show "Family Guy" is forever young. His age is still determined.
Stewie Griffin, the cunning infant prodigy, is impossible to determine from the world. Speculation runs rampant as to the length of time he has existed. Is he over a hundred years old? Or is he fresh to the world? The answer is known only to Stewie! This enchanting character continues to mesmerize fans with his undisclosed age and perpetually youthful visage.

List of Family Guy cast members Wikipedia