No, equal protection would mean that anyone who has sex with someone over 18 would be okay. You can NOT make it a felony only if you are a teacher.
You obviously do not understand equal protection. Other than a few prohibited reasons, race, sex, religion, etc, the states can discriminate all they want based on "status". Age is a just a status issue itself. As long as the law applies to everyone with the same status, then it's not an equal protection violation