Whoever, being at least 4 years older than a child, engages in a sexual act with that child or causes that child to engage in a sexual act shall be imprisoned for any term of years or for life and, in addition, may be fined not more than the amount set forth in § 22-3571.01. However, the court may impose a prison sentence in excess of 30 years only in accordance with § 22-3020 or § 24-403.01(b-2). For purposes of imprisonment following revocation of release authorized by § 24-403.01(b)(7), the offense defined by this section is a Class A felony.