He literally hasn't aged a day since the show began but in reality, Family Guy's Peter Griffin should be pushing 60 years old about now. Family Guy was created by Seth MacFarlane (Ted) and follows Peter Griffin and his family, including wife Lois and children Chris, Meg, and Stewie. Peter can be extremely selfish, impulsive, and offensive, but he's also capable of being sweet and cares deeply for his family and friends - even if he doesn't always behave that way.
Family Guy quickly became a cult show following its 1999 debut, but it was canceled at the end of its third season due to disappointing ratings. The show's popularity only continued to grow thanks to reruns and DVD, so it was revived in 2005 and has been running ever since. The show is set to return for season 18 and a movie is in development.
Family Guy has been around for over 20 years now, but while Peter looks permanently about 42, according to the timeline he should be close to 60. Lois once stated she was two years younger than Peter, making her around 58 while Stewie, who should really be about 20, is still a baby. Of course, Family Guy is a cartoon, so realism doesn't really need to enter the frame.
That's because Family Guy, like The Simpsons, South Park or any number of long-running animated shows, operate within a floating timeline logic often used in cartoons or comics. Homer Simpson should logically be about 65 years old, but while the timeline of The Simpsons has always been somewhat messy, he visibly hasn't changed in any significant way since 1989.
In addition to just making the shows easier to animate, since the character's appearance or clothes never change, it avoids any pitfalls involved with trying to pay strict attention to the passage of time. This also allows series like Family Guy and The Simpsons to include real-life or modern day events without breaking the timeline. Of course, fans can be snarky about this as a device, and Family Guy itself has poked fun about these inconsistencies more than once, but its a necessary evil.
Its doubtful heroes like Batman or Spider-Man would still be fighting crime if their comics had to follow a strict passage of time either. That said, there are some shows and comics that acknowledge the passage of time, including BoJack Horseman or Judge Dredd, with the Mega-City One lawman now in his seventies. Family Guy is unlikely to adopt such an approach after two decades, meaning Peter Griffin wouldn't be updating his look anytime soon.