In the State of Ohio, after turning 18 years old, can truancy officers still file charges of truancy should a person not show up to school?

No, but if caught you can be expelled per the rules of the school enrolled. And at 18 the local school system is under no obligation to replace you within the system the following semester or school year like they are for minors.

i'm told that you simply flunk all classes for non-attendance

So the truancy officers in Ohio are under 18 years old? That makes no sense at all.

Yes

No

Nobody cares. For that matter most schools don't have truancy officers at all. This is just a law to round up loose kids in the middle of the day and fine their parents.

The cool part is once they decide you're not attending anymore, they don't have to waste money on you and can ban you from the premises.

You can quit school, previous to 18 charges can still be prosecuted and a judge can order you to stay in school. New charges cannot be filed.

"File charges?" Sure. If you are trying to ask about the results of that act, try again.