If a person starts school at age 17 and turns 18 during the school year can the person be charged for not attending school under Chapter 25.085 (compulsory school attendance), after turning 18?

The Section you asked about Ed. Code Sec. 25.085(e) says as follows: A person who voluntarily enrolls in school or
voluntarily attends school after the person's 18th birthday shall
attend school each school day for the entire period the program of
instruction is offered. A school district may revoke for the
remainder of the school year the enrollment of a person who has more
than five absences in a semester that are not excused under Section
25.087. A person whose enrollment is revoked under this subsection
may be considered an unauthorized person on school district grounds
for purposes of Section 37.107.

This has been interpreted to mean that the student IF HE VOLUNTARILY ENROLLS OR ATTENDS must complete the academic year or he will be in violation. So, yes he can be charged. The juvenile court doesn't have jurisdiction because he's over 17.