Dear Vartika, the eligiility criteria for AIIMS 2019 are:

1. You should have had minimum 17 years of age or will complete 17 by December 31st 2019.

2. You should have passed 12th from any recognised board or University with Physics, Chemistry, Biology and English as core subjects.

3. 60% marks in your 12th for OBC/General and for SC/ST/OBC it is 50%.

4. You should be an Indian Citizen. Overseas Candidates and NRIs are also eligible. 

However the criteria donot talk about the educational gap. I would suggest you to AIIMS MBBS helpline at aiims.mbbs18@gmail.com.