hi neelam, the good news is there no limit on the number of attempts you can give for all india institute of medical sciences.

The All India Institute of Medical Sciences, New Delhi conducts AIIMS MBBS 2017 for providing admissions to as many as 707 MBBS seats in 7 AIIMS institutes located in the country,This year, AIIMS MBBS 2017 is scheduled to be conducted on May 28, 2017 in a computer based mode for admissions to AIIMS institutes located at New Delhi, Jodhpur, Rishikesh, Patna, Bhubaneswar and Raipur. hope this helps, good luck 

Student can attempt the AIIMS MBBS entrance end number of times as there is no bar in the same but the minimum age limit should be 17 years, 60% should be there in PCBE in 12th. To check the complete eligibility, you can go through the below link-

https://medicine.careers360.com/articles/aiims-mbbs-eligibility-criteria

Good Luck!!!