Dear Dhamik, for NEET 2019, candidates with a gap year have been allowed to attempt NEET. Assuming the rules for 2021 is difficult. However, the basic criteria would remain the same. 10+2 with Physics, Chemistry, Biology/Biotechnology and English as core subjects, minimum 17 years of age and minimum qualifying percentage. So I would suggest you to watch out for the criteria when released in next year for AIIMS or for NEET in 2021.