It’s pretty much locked in once you hit your teens. You can nudge it a little, you can change how you present yourself but your personality is what you are. And you cannot change that significantly. Just try changing your core values, your ethics. Can you start believing and feeling like murder and rape is ethical?

I’m not sure how accurate this is but I’ve read it in a scientific article some time ago. In particular, it highlighted the connection to how likely people are to commit crimes based on personality and brain structure alone and whether you can actually be held responsible for crimes since there is at least some determinism.