A person is guilty of criminal sexual act in the second degree when:

1. being eighteen years old or more, he or she engages in oral sexual conduct or anal sexual conduct with another person less than fifteen years old; or

2. he or she engages in oral sexual conduct or anal sexual conduct with another person who is incapable of consent by reason of being mentally disabled or mentally incapacitated.

It shall be an affirmative defense to the crime of criminal sexual act in the second degree as defined in subdivision one of this section that the defendant was less than four years older than the victim at the time of the act.

Criminal sexual act in the second degree is a class D felony.