I think Trevor is writing about growing up and how much a person changes between their teenage years and early 20s. At 9, he had a poster, doesn't matter what kind of poster it was, just that it was an inspiration for him, something that he wanted to emulate or become. As he grows up, he accumulates more posters on his walls, which represents more goals, ambitions, and dreams to drive him. Yet, with all these ambitions and idols that he wishes to emulate, Trevor still felt like he didn't know who he was as a person, and what drove him to be the way he is. When he says "my whole wall is filled with posters, my whole life is filled with posters", I think he's moving forward in his life again to the period when he had become a musician and was starting to play organized shows, and the "posters" he's referring to are all the flyers from his shows and other artists shows that he looks up to. He's basically saying that his interests and desires have become his life.
As for the last part of the song, I think he's talking to a family member or former childhood friend. He was brash in his youth, doing anything to garner attention, but he's grown out of that now, and is much more self reflective. So that person he's talking to wonders what's happened to the Trevor they knew, and he's telling them that he's different now, and that he's finally found himself (aka comfortable with himself, does not need others approval).
I think Trevor is writing about growing up and how much a person changes between their teenage years and early 20s. At 9, he had a poster, doesn't matter what kind of poster it was, just that it was an inspiration for him, something that he wanted to emulate or become. As he grows up, he accumulates more posters on his walls, which represents more goals, ambitions, and dreams to drive him. Yet, with all these ambitions and idols that he wishes to emulate, Trevor still felt like he didn't know who he was as a person, and what drove him to be the way he is. When he says "my whole wall is filled with posters, my whole life is filled with posters", I think he's moving forward in his life again to the period when he had become a musician and was starting to play organized shows, and the "posters" he's referring to are all the flyers from his shows and other artists shows that he looks up to. He's basically saying that his interests and desires have become his life.
As for the last part of the song, I think he's talking to a family member or former childhood friend. He was brash in his youth, doing anything to garner attention, but he's grown out of that now, and is much more self reflective. So that person he's talking to wonders what's happened to the Trevor they knew, and he's telling them that he's different now, and that he's finally found himself (aka comfortable with himself, does not need others approval).