Hi! CAS po (Centenarian or senior citizen ID) usually gets processed sa Municipal Health Office or sa barangay hall mo, best to call them directly kasi bawat municipality may sariling requirements at schedule, lalo na sa Zambales area kaya hindi ako sure ng exact process doon, sorry! One of my mum friends had to bring original documents ng birth certificate at medical certification, pero I'd really recommend asking directly sa health office ninyo para sure sa requirements.