If you are writing from a eight-year-old's point of view, would you use words like complexity, sadistic, indecisive, and metamorphosis?
No, you would use complicated, crazy/evil, can't choose, and change.
Language is a major part of believable writing.
For Childish Characters:
Use words that are simple.
For Teen Characters:
Use slightly more complex words, or if your character is really smart, then go ahead and use that brain!
For Adult Characters:
Language here is dependent on the personality. If your person is studious, then of course they have a bigger vocabulary.
