For the purposes of determining whether a child was dependent upon
a deceased miner, the provisions of Sec. 725.209 shall be applicable,
except that for purposes of determining the eligibility of a child who
is under a disability as defined in section 223(d) of the Social
Security Act, such disability must have begun before the child attained
age 22, or in the case of a student, before the child ceased to be a
student.