You can register to vote if you are a  citizen of the United States, a resident of the State of Oklahoma, and  at least 18 years old or meet the age requirement to pre-register.

• Pre-registration -  Persons who are at least 17½ years old may pre-register to vote in  Oklahoma if they meet all eligibility requirements. Applicants  who preregister cannot vote until they turn 18 years old and  the application has been approved by the applicant's County Election  Board. Applicants will be mailed a voter ID card upon approval of their  registration. Applications received less than 25 days before an  election, in which the applicant has turned 18 and is eligible to vote,  will be held and processed immediately following the election. 
  
• Persons Convicted of a Felony  – A person convicted of a felony may register to vote when he or she  has fully served his or her sentence of court-mandated calendar days,  including any term of incarceration, parole or supervision, or completed  a period of probation ordered by any court. A convicted felon who has been pardoned may register.
  
• Persons Judged Incapacitated - Persons judged incapacitated by a court may not register to vote.

You may submit your voter registration application at any time. However,  the voter registration deadline is 25 days prior to the date of an election. You can find the dates of voter registration deadline here.

Mailed  applications that are postmarked 24 or fewer days prior to the date of  the election, or hand-delivered applications that are received by  election officials or voter registration agencies 24 or fewer days prior  to the date of the election, or electronic updates to a voter  registration that are submitted 24 or fewer days prior to the date of  the election, will be processed after that election.

If  you pre-register to vote, you will be mailed a voter identification  card once you turn eighteen and your registration has been approved and  activated by the county election board.