For many of the side characters, we just don't know. However, we've got a pretty good idea of the ages of the main crew, thanks to episodes that reference their ages.In the season one episode "Some Enchanted Evening," Marge calls into a radio show hosted by Dr. Marvin Monroe; he introduces her by saying, "Next we have Marge. She's 34 and trapped in a loveless sham of a marriage." Later in that season, Marge has a birthday, but as we'll discuss in a moment, birthdays don't really change anything in The Simpsons universe.In the season three episode "Radio Bart," the family celebrates Bart's 10th birthday. Mr. Burns also notes that Bart's 10 years old in the season three episode "Bart the Murderer."Lisa also celebrates her 8th birthday in season three ("Stark Raving Dad"), writing a poem called "Meditations on Turning Eight." Maggie celebrates her first birthday in Season 5's "Lady Bouvier's Lover," and has been one year old ever since.For others, we have to make educated guesses, as their ages aren't consistent throughout the series. Homer, for instance, is somewhere in his late 30s. In the 1993 episode "Duffless," Homer shows his license, which declares his age as 36, but he's 39 in the season eight episode "The Homer They Fall." In a DVD commentary, former showrunners Bill Oakley and Josh Weinstein say that Homer's age increased to 38 during their time on the show.Abe Simpson, Homer's father, is shown to be 83 in the season 17 episode "Million-Dollar Abie." In the season 29 episode "Grampy Can Ya Hear Me," however, the Simpsons celebrate Abe's 87th birthday.Mr. Burns is probably in his 80s, but his exact birth year varies from one episode to the next, depending on what the plot (or the gag) calls for. He's shown to be 81 in the episode "Simpson and Delilah," but he's 104 in "Who Shot Mr. Burns? (Part One)" and in several other episodes.If the Simpsons aged normally, the show would be considerably different in 2019; using their ages at the start of the show's run, and noting that the first episode aired on Dec. 17, 1989, Marge would be 63, Homer would be 65, Maggie would be 30, Lisa would be 37, and Bart would be 39.Of course, that's not the case, as the characters' ages are (mostly) locked in place. The world around them, however, is not. Throughout the show, the Simpsons have encountered different U.S. presidents and adapted to changes in technology. That doesn't mean that Bart is secretly in his 30s--the rules for Cartoons are, of course, different. No matter how long the show runs, the family will stay the same.That's called a "floating timeline," and it's pretty common in cartoons; the boys in South Park, for instance, are perpetually grade schoolers, although they've occasionally moved up a grade over the course of the show.Will that ever change for The Simpsons? Probably not--but show creator Matt Groening won't rule it out entirely."We may [age the characters] when we run out of ideas," he said at 2011's Comic-Con. "That may be the last sad season of The Simpsons. Bart will turn 11."