I like to think of AT as a show about growing up and maturing. In the first seasons, we see an immature 12 year old punching things to solve all his problems, trying to hook up with his baby sitter/mother figure as he doesn’t understand that the relationship would never work out. The kid is a puppy dog, rarely questioning authority and beating up the “bad” guys with little remorse.
By the end of the series, Finn has done a 180. He progressively starts challenging Bubblegum more till they are on equal footing. Ice King goes from a villain to pound on, to a sick man that Finn has learned to deal with in non-lethal ways. By the end, Finn is the one being the adult and trying to resolve conflicts through talking, while his adult figures act way more immature.
I like how the show progressively matures Finn. He grows to get over Bubblegum. He then has a relationship with FP, but being immature at the time, manages to mess up and hurt her. Episodes like All the Little People, Fire and Ice and Another Way, depict Finn’s early immaturity in a dark way. He tries to meddle with people without understanding the consequences, only to then get burned and have to live with the horrid things he has done. This is then capitalized on in later seasons with Finn making up with FP, but not getting back together. He instead makes a mature apology and they learn to respect each other, while acknowledging the damage cannot be undone. Finn also Carrie’s these lessons into his relationship with Huntress Wizard, choosing to let things play out rather than forcing a relationship to complete himself.
Finn’s relationship with the Ice King is another strong point. He goes from pounding on him to progressively getting softer. I like how in later seasons, Finn grounds him or puts a dirty sock on his nose rather than punching him. It shows how much he has matured and acknowledges Ice King for the mentally unwell man he is. Simon cannot control his actions, and learning that, Finn (along with Marceline and others) learn to accommodate him more.
For further examples of maturity, the end of season 6 gives Finn an ultimatum. He can live on Ooo or transcend to Godhood and live forever. In earlier seasons, Finn likely would have become a God, but by season 6, Finn understands the world more, and decides that living with purpose and companionship is more important. By the end of the series, the distinctions really become apparent as Finn, the once child that beat things up, argues with “mature” Bubblegum over not starting a war and just trying to work her family problems out.
I really appreciate Finn’s journey throughout the show. It is on of AT’s strongest points as we follow this child grow and start seeing his wacky world from a different point of view. I know people hate how he didn’t end up with someone, but it feels semi-fitting given all the build up. Finn learned to live with himself and his friends, maturing past them in many ways. He didn’t need a partner by that point.