A person is guilty of rape in the second degree when:

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

2. he or she engages in sexual intercourse 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 rape 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.

Rape in the second degree is a class D felony.