Since we don't know what his personality was in his yunger years, we don't know if it changed. As you live your life you encounter different situations to which you react with the tools you have. As time goes by, you gain experience. One experieince is the realization that you get one life to live - that's all.
We know a little about him. He grew up in a two mule town in Sicily. He must have been in his late teens or even early twentieswhen he came to the US because we know that his brother decided to stay in Sicily, and never wanted to come here. So if he spent his formative years there, he probably got "connected" and perhaps had something to do with Don Tomassino who sent him to America to start with the Corleones. This may mean he had little or no formal education other than grade school in Sicily.
He was probably self taught in English, and eventually became a voracious reader. But nevertheless he didn't have a brain for big deals.
