As he continues through the stages of age, his personality gets different. It's pretty much character development and how much he's changed.

As a child he was innocent, shy and happy

As a teen he was still innocent, shy but was sad. And then he gained a phobia of being touched.

When running away from home at the age of 19, he stopped being sad but was so happy and excitable, he seemed nuts. That's when he grew out of shyness.

In his early adulthood he gained a quick temper while paranoid and scared. Not acting happy but constantly upset in either anger or paranoid fear.

When becoming a god, he was happy to finally have power. He stopped being paranoid, angry and was so happy. He got over his phobia too.

Many, many years later and certain events occurred which traumatized him. He still acted happy but he seemed to go crazy while having a temper problem again. Along with being both emotionally and mentally unstable. He gained a phobia of being overpowered to the point he'd freak out if he felt the slightest bit at a disadvantage.

It's mostly Greed's fault for the trauma and unstable behavior.