A person who commits statutory sexual seduction shall be punished: If the person is 21 or older at the time of the offense, for a category B felony and prison for 1 to 10 years, and may be further punished by a fine of up to $10,000. If the person is under 21, for a gross misdemeanor unless he has previously been convicted of a sexual offense, as defined in NRS 179D.097. If a person has been previously convicted of a sexual offense, then for a category D felony as provided in NRS 193.130.