Hi aspirant

hope you are doing absolutely fine.

Yes it is mandatory to have valid ST or any other caste certificate. The documents are required at the time for admission nd counselling as well. here is the documents required-

• Candidate’s passport size photograph

• scanned signature

• Left-hand thumb impression

• Class 10 mark sheet

• Class 10 Passing Certificate

• Class 12 mark sheet

• Class 12 Passing Certificate

• ID proof for example, Adhaar Card

• Here is the eligibility for AIIMS-
  
  Candidate must secure minimum of 60% aggregate in 10 + 2 higher secondary education from a recognized college/ university.
• The subjects in 10 + 2 higher secondary must be physics, chemistry and biology

all the best

hope it helps