Freshman can take IELTS: no matter how old you are, you can take IELTS. Many high school students have gone abroad now. Under special circumstances, if you are under 18 years old and need a guardian to sign a document, you can take the exam when you are over 18 years old. There are no other requirements.
IELTS preparation: If you want to take the IELTS test, you need to know the IELTS test first, and you don't need to learn the basic knowledge of IELTS. After all, IELTS is different from our college entrance examination English, CET-4 and CET-6, and knowing more is twice the result with half the effort.