Md. Code, Family Law § 5–4C–05

Only the following individuals may register with the Registry:

(1) an adoptee:

(i) who is at least 21 years of age; and

(ii) who does not have a natural sibling under the age of 21 years who has the same adoptive parents;

(2) a natural mother;

(3) a natural father; and

(4) a natural sibling.