I am writing a piece which features two POV characters. A conceit of the story is that the POVs are writing their chapters, so each one reflects not just their personality, but how my characters would actually write.

One of my POVs is very sophisticated and cultured, and I have endowed his writing with complex sentences and sesquipedalian words and fancy references.

The other character however, is not a native English speaker (though she is fluent), and an average high school student in terms of writing ability. in addition, I want her writing to have an informal, almost conversational tone. Her chapters have been difficult to write, because I tend towards complex sentences and fancy references. As a preliminary step, I've tried banning semicolons from her writing, but I often find myself re-reading my own work and thinking, "No 18 year old would write this."

How can I ensure this character's writing is age and background appropriate, when my own writing is very different?