At a primary election every qualified elector who is or will be on the day of the next general election eighteen or more years of age, and who is a member of or is affiliated with the political party whose primary election ballot he desires to vote, shall be entitled to vote such ballot at the primary election.
Qualifications of electors for primary elections
Ohio Rev. Code Ann. § 3503.011, under Chapter 3503 | Voters - Qualifications; Registration.
Ohio Rev. Code Ann. § 3503.011