I want to know if there is any new rule that after 12th, students can not go for IELTS? Do the students have to first complete graduation in India?

IELTS can be given after 12th. The only eligibility for the IELTS exam in India and across the globe is that a candidate needs to be at least 16 years. Anybody aged 16 or above can take this examination, irrespective of their gender, nationality, or background. Exceptions are only made when a school needs the IELTS scores for admission purposes.

Any candidate can appear for the IELTS test, irrespective of their age, gender, nationality or academic background for 

admissions in IELTS participating universities or immigration purposes. 

There is no upper age limit to appear in the test. However, it is not recommended to be taken by any person under the age of 16 years at the time of the test.

English language proficiency is a student visa requirement and getting into a university has no impact because of this. Those who do not want to give IELTS or any other English language proficiency test can now apply to universities that offer admission without asking for IELTS exam scores. However, there can be other criteria set by the university which you need to fulfill to secure admission. UK universities may ask students to prove their English language proficiency not with the standardized tests score but in a different way. So, you can check with the university how it is measuring your English proficiency, thus saving your time, money, and efforts all at once.