With all the anarchy in the Gallagher household, it can be difficult to keep track of how old the characters in Shameless are from the beginning to the end of the show. When the comedy-drama series debuted on Showtime in 2011, all of the Gallagher kids (except for Fiona) were still minors. By the time the series wrapped up with the season 11 finale in the spring of 2021, all except Liam are adults with jobs and - in some cases - kids of their own.
Monica Gallagher had six children altogether before walking out on the family and leaving Fiona to take on the brunt of the parenting (even more so than she already had). In a rant in season 1, Frank helpfully spells out the age differences between the kids, saying that Monica left when Fiona was 14, Lip was 11, Ian was 10, Debbie was seven, Carl was five, and Liam was four months old. Of course, this being Frank, there's probably some room for error in his calculation of the kids' ages. Other clues in the show indicate that Fiona is actually around five years older than Lip, not three.
The Shameless timeline is notoriously riddled with continuity issues, which often makes it difficult to keep track of how much time passes between seasons and how old the various characters are. In an interview with EW, creator John Wells joked that the show is written on "Shameless time," with some characters' storylines taking place over a few days while others take place over several weeks. However, thanks to mentions of their age in dialogue it's possible to pin down their ages when the story begins, and how old they are when things wrap up in the Shameless season 11 finale.
In Shameless season 1, Fiona is 21 years old, Lip is 16, Ian is 15, Debbie is 11, Carl is nine, and Liam is around 18 months old. Debbie's daughter Franny, who was born when Debbie was 15, celebrates her fifth birthday in Shameless season 11, at which point Liam is about 11 years old. Putting these details together, it appears that around nine years pass between the start of Shameless season 1 and the end of season 11. By the time of the series finale, Fiona is 30, Lip is 25, Ian is 24, Debbie is 20, Carl is 18, and Liam is 11 years old. It should be noted that all of these ages are approximate, and could vary by a year or so. This is due to the show not only operating on its own time, but Shameless' status as a TV series means that the number of seasons doesn't always equate to the number of years that have passed since its debut. And because of the occasional continuity issues, it wasn't always clear how old the characters were at certain points. However, there were enough clues and information given so that the ages were clearer by the end of Shameless' run.
By the end of Shameless season 11 the Gallagher family got even bigger. Mickey Milkovich is around the same age as Lip Gallagher, which would make him around 25 years old when the story ends. As mentioned above, Debbie's daughter Franny is five years old, having been born on the Gallaghers' kitchen table in season 6. Lip's son, Freddie, was born in the first episode of season 10 and therefore must be at least a year old by the series finale, since Ian and Mickey are celebrating the one-year anniversary of their wedding from the end of season 10. Fred is probably about the same age in the finale as Liam was at the start of Shameless season 1. That essentially brings the Gallagher household full circle with regards to their ages, as another generation is born.
Moving next door, Kevin and Veronica's ages are never explicitly given at any point in the series, but they appear to be in their mid-to-late 20s in Shameless season 1. That puts them in their mid-to-late 30s by the time they pack up and get ready to move to Louisville in Shameless season 11. Their twin daughters, Amy and Jemma, were born in the season 4 finale, and Franny was conceived just a few episodes later, which means that Kevin and Veronica's twins are about 6 years old by the end of the series.