As you have not mentioned the name of the exam whose criteria you want I will answer in general. If you are talking about JEE-Mains criteria-

1)Candidate should have passed class 12 or qualifying the exam in 2019 or 2020.

2)Candidates appearing in class 12 or equivalent qualifying exam in 2021 can also apply for JEE Main 2021. https://engineering.careers360.com/articles/jee-main-eligibility-criteria

B)NEET-

1)Students must have passed 10+2 or equivalent with Physics, Chemistry, Biology/Biotechnology and English as core subjects from a recognized board. Class 12 or equivalent students are also eligible. Minimum candidate age should be 17 years( https://medicine.careers360.com/articles/neet-eligibility-criteria )