Dear Manju, the upper limit condition has been put on hold atleast for now. Candidates should be 17 years atleast by December 31st of the year of admission. This is the age criteria. For Academic eligibility, you should have completed your 10+2 with a minimum aggregate of 60% in Physics, Chemistry, Biology and English. 60% is for General Category. 

There is a lower age limit of 17 years but there is no upper age limit to join AIIMS for MBBS as mentioned on their website. So I believe that as long as you meet the minimum academic percentage criteria and score the cut off marks in the entrance exam, you are great to go.

You can check the link below - 

http://mbbs.aiimsexams.org/Home/Eligibility