Exactly. I understand why, for example, the Beast from Beauty and the Beast is an immature little asshole at the start; because he was a spoilt kid turned into a monster that prevented any kind of human contact.

Edward though? He's lived through the most active and world-changing century in history. He could have been a vampiric Forrest Gump, seeing all these amazing events and changing as a person because of it.

Even if he's stuck as a teen, he'd sure as hell should be a mature and wise teen.