We could talk for hours abt Edward Elric’s refusal to treat himself like a child and yknow what its his birthday SO.
Edward very much had to grow up from the moment their mom died
He was already pretty mature for like, a literal baby, since he was going around mastering complex scientific concepts and deciphering his dad's alchemy journals before their mom died, but once she was gone he had to be the adult of the family. Pinako was there to keep them fed, but Edward had to make sure the house was taken care of. Make sure Al was safe, bathed, clean, had clothes to wear and went to school every day, make sure Al felt safe.
He very much took on the role of an adult before he was ready for it, and the reason he acts like a maniac and swears so much is because that is what a little kid thinks an adult is like. They don't really understand yet what it fully means to be an adult, so Edward emulated the things that he thought adults did. Swearing, taking on responsibility for everything, and fighting first asking questions later. He's like this even now, at 16, both because hormonal teens tend to be like that and because he essentially stunted his own emotional growth by forcing himself to act like what he thought an adult was from a very young age.
(What little we see of him before Trisha dies he doesn't act like this at all. He's a sweet little kid. He's mean to Al at first, but only until she gives him the "protect your little brother lecture." He starts acting cynical and rude after she dies because he's trying to become an adult for Al's sake!!!)
On the other side, Al is very much the opposite. He's sweet and kind, not only because he didn't have to force himself to emulate an adult for the sake of a little brother, but because he saw Edward doing that and decided that it was his job to be the voice of reason and the one to take care of Edward when Edward didn't take care of himself. Alphonse is the one who knows Ed's kindness best, and that's the part of his brother that Al looks up to the most and the part that he seeks to emulate. Other than that, you can really see so much of their mother in Alphonse. He remembers her and emulates her as he grows up because he loves her, and what he sees of her in Ed is what he really wants to emulate of Ed, and what he wants Ed to be like.
They say that automail stunts growth (physical growth) but at the same time, the incident that gave Edward his automail stunted his emotional growth, and once he's free of the automail arm he's also free of the guilt that's been weighing him down, and he's free to grow taller (physically) and grow into a much calmer happier person emotionally.
(03 has a different, much bleaker and more upsetting resolution to their codependence. But hey, at least they get to be happy in one version of the story—)
