Showtime's Shameless is the network's longest-running series to date, with 11 seasons following the chaotic Gallagher kids while they try to hold their family together. The drama premiered in 2011, and in between making sure none of the siblings ended up in jail or worse, while their addict father stole from them, the Gallagher kids grew up.
The kind of situations that this group of kids went through can be hard to fathom if we understand how a barely adult Fiona was taking care of her siblings, better than either of their parents did, when the show aired its first season. Here is how old the main characters were in Shameless Season 1.
How old were Fiona and the other main characters in Shameless Season 1
Fiona Gallagher, played by Emmy Rossum

The eldest of the Gallagher kids, Fiona, is one of the most favorite characters on Shameless, owing to her tenacity and determination. She was basically a mother to the Gallagher kids, and despite being fairly young herself, she worked odd jobs and skipped her education to ensure that her siblings were able to make something of themselves in their lives.
Fiona was 21 years old in the first season, and the actress who played her, Emmy Rossum, was 25 when the show premiered.
Lip Gallagher, played by Jeremy Allen White

Even though Fiona had to drop everything at 16 when Monica walked out on the kids, Lip was the only one who had a clear way of making it out of the place successfully, being the smartest of all the Gallagher siblings. He had a genius-level IQ, and even though it took a lot, he ended up at college. However, being himself, he was irresponsible and self-destructive and ended up ruining that opportunity for himself.
When Season 1 aired, Lip was only 16, and even though he was 5 years younger than Fiona, he helped her out a lot with the other siblings who were younger than him. Jeremy Allen White was 20 when Shameless Season 1 first premiered on Showtime.
Ian Gallagher, played by Cameron Monaghan

Ian had one of the most tragic stories out of all the Gallagher kids, as even though he started out on a very determined path, he inherited a lot of mental issues from their mother, Monica, and went through a lot just to stay alive. Ian was only 15 when the show first premiered, and Cameron Monaghan, who played him, was about 18 at the time of the premiere.
Debbie Gallagher, played by Emma Rose Kenney

When Shameless Season 1 premiered, Debbie was only 11, and the absolute picture of innocence. We watch her heart get broken when Frank fails to be a father and Monica a mother, but there's still an innocence in her. However, as the series progresses, she ends up on a path opposite to her younger self. She has a baby at just 15 and ends up performing criminal activities, one after the other, after she has Franny. Emma Rose Kenney was only 12 when the show first premiered.
Carl Gallagher, played by Ethan Cutkosky

The second youngest Gallagher kid, Carl, has one of the most interesting storylines. He has a wild streak about him, which we discover when he becomes a drug trafficker and then goes off to military school, and then goes on to become a policeman. Carl's arc is one of the most loved among all the Gallagher kids, especially considering he was almost a drug-selling gangster by the time he turned 10. Carl was 9 in Shameless Season 1, and Ethan Cutkosky, who played him, was about 12 at the time of the show's premiere.
Liam Gallagher, played by Christian Isaiah

The youngest Gallagher kid was only an eighteen-month-old toddler when Shameless Season 1 premiered and was recast thrice during the run of the show, as the character grew older. Since Liam was the youngest, he didn't harbor the resentment against Frank for being absent from their lives, like the other kids, and was still willing to give him a chance to be a father. Liam was Frank's only chance to be a good father, and even though he was rarely good at it, he still tried.
Among other characters on Shameless, Frank Gallagher, played by William H. Macy, was 57 at the time of the show's premiere, and Kevin and Veronica were somewhere in their 20s as well.
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