(a) A person is guilty of sexual assault in the third degree when:
(1) The person engages in sexual intercourse or sexual intrusion with another person who is mentally defective or mentally incapacitated; or
(2) The person, being sixteen years old or more, engages in sexual intercourse or sexual intrusion with another person who is less than sixteen years old and who is at least four years younger than the defendant and is not married to the defendant.
(b) Any person violating the provisions of this section is guilty of a felony and, upon conviction thereof, shall be imprisoned in a state correctional facility not less than one year nor more than five years, or fined not more than $10,000 and imprisoned in a state correctional facility not less than one year nor more than five years.