http://www.oklahomalegalgroup.com/ageofconsent
Don’t know where you’re getting your information but the age of consent in Oklahoma is 16.
If you are over 18 and have sex with a girl 14 or less it’s a 1st degree rape, 14-15 2nd degree.
Actually, I used the very site you provided in your link, but upon further research, I think it needs better clarification.
I took this, from the link you provided: "In Oklahoma, the age of consent is 16, and the law recognizes an age differential of two years. This means that no person can be convicted of rape or rape by instrumentation with anyone over the age of 14, with that person’s consent, unless the defendant was older than 18 at the time the sexual act occurred. Though statutory rape is a strict liability crime which does not require the prosecutor to prove that an assault occurred, it is still classified as rape under the Oklahoma penal code."
I took it to mean that if the defendant was over 18, even if the victim was 16, that statutory rape had occurred. However, upon finding further information, it's muddled, and that over 18 appears to only apply if the victim is younger than 14, depending on how it's read. So, it's best to practice that age-old advice that 16 will get you 20, and stay the heck away.