You don’t have to study drama or performance academically before applying to drama school, but you should get as much practical experience as possible, whether work placements or youth theatre. If you can, watch live theatre regularly and read as many plays and books as possible. Though there are educational options available, doing these things could provide you with as rich an experience as any course.
If you’re at school, know you want to become an actor and are intending on applying to drama school, there are opportunities to study drama academically in the meantime. Some drama schools have specific entry requirements (typically 5 GCSE and 2 A-level passes or successful completion of a relevant BTEC course) so researching courses at an early stage is important.