Is it illegal for a 16 year old to date and have sex with a 41 year old when the parents of the 16 year old agree to let them see each other? what is the penalty if it is a crime

The age at which a minor may consent to a sexual act in the state of Oklahoma is 16. However, in the scenario you describe there are area's within Oklahoma law where this may be considered a ciminal act. More detail and a consultation with a lisenced attorney in the state of Oklahoma would be highly recommended prior to sexual involvement with a minor. Upon conviction, it would be deemed a felony and the penalty could range between 1-20 year prison sentence.