/kloc-What should I do if I am not allowed to apply for a health certificate under 0/6 years old?

Take the account book and say it. There is no age limit for applying for a health certificate, but you need to verify your personal identity before you can legally apply for it. If you have an ID card, you can use it to verify your identity. If you don't have an ID card, you can apply for it with a household registration book, and then explain the purpose of applying for a health certificate.