Except as provided in sub. (13) (b), the parent of a dependent person who is under the age of 18 and is alleged to be the father of a child is responsible for maintenance of that child only if the paternity of the child has been determined to be that of the dependent person as provided in subch. VIII of ch. 48 or under subch. IX of ch. 767. Subject to the limitations under sub. (1) (a), if a parent of a dependent person is liable for the health care expenses of the dependent person’s child under sub. (4), this liability extends to all expenses of the child’s medical care and treatment, including those associated with the childbirth, regardless of whether they were incurred prior to the determination of paternity and regardless of whether the determination of paternity is made after the child’s father attains 18 years of age, except that the period for which maintenance payment is ordered for the parent of a dependent person may not extend beyond the date on which the dependent person attains 18 years of age. The court may limit the liability of the dependent person’s parent for the child’s medical expenses if the expenses exceed 5 percent of the parent’s federal adjusted gross income for the previous taxable year, if the parent files separately, or 5 percent of the sum of the parents’ federal adjusted gross income for the previous taxable year, if the parents file jointly.