Until 1907, Garvin County was included in the Chickasaw Nation of Oklahoma Indian Territory.I think I have located the marriage that you are wanting but keep in mind that these marriages have been transcribed and the spelling may not be exactly correct:
Marriage Book D, page 407, Chickasaw Nation, I.T.
J. J. Steel age 21 to Ada Johnston age 16 December 7, 1899 at Roberson.
I am sure that you are aware that many girls did not give their correct age.If you obtain the actual marriage record, it might show who gave approval for this marriage.