This report is available in the Report Center and shows patients (who are 17) whose 18th birthdays will be in the month following the selected date range.
Navigate to Reports | Report Center
Select "Under Age Patients" report
Enter BirthDate Range, Start Date and End Date of month(s) prior to patient(s)18th birthday.
Click Run Report
See example of one month's data.
See example of multiple month's data.