Section 12(3) in The Juvenile Justice (Care And Protection Of Children) Rules, 2007
(3) In every case concerning a child or juvenile in conflict with law, the age determination inquiry shall be conducted by the Court or the Board or, as the case may be, the Committee by seeking evidence by obtaining: -
(a) (i) the matriculation or equivalent certificates, if available; and in the absence whereof;
(ii) the date of birth certificate from the school (other than a play school) first attended; and in the absence whereof;
(iii) the birth certificate given by a corporation or a municipal authority or a panchayat;
(b) and only in the absence of either (i), (ii) or (iii) of clause (a) above, the medical opinion will be sought from a duly constituted Medical Board, which will declare the age of the juvenile or child. In case exact assessment of the age cannot be done, the Court or the Board or, as the case may be, the Committee, for the reasons to be recorded by them, may, if considered necessary, give benefit to the child or juvenile by considering his/her age on lower side within the margin of one year, and, while passing orders in such case shall, after taking into consideration such evidence as may be available, or the medical opinion, as the case may be, record a finding in respect of his age and either of the evidence specified in any of the clauses (a)(i), (ii), (iii) or in the absence whereof, clause (b) shall be the conclusive proof of the age as regards such child or the juvenile in conflict with law.