Listen, it just has to be something that you can make sound interesting and entertaining in a way that is cast-able for any characters in the play or company you are auditioning for.
If you can make a recipe for a peanut butter and jelly sandwich interesting, then that should be your monologue.
Again, the only thing you need to know is this:
1) Age Appropriate
2) YOU can make it Entertaining (relatable through an emotional connection)
3) You are the only one needed