I would think of it like this- If the job on paper requires you to be a high school graduate, you're overqualified because you have education beyond high schoo

I would think of it like this- If the job on paper requires you to be a high school graduate, you're overqualified because you have education beyond high school. If the job requires vocational training/certification/licenses/experience etc, that's a different story. The fact that you wouldn't be that good at the job in practice doesn't mean you're not overqualified.