There are various reports you can use in order to obtain student ages and their birth dates.
Go to Reporting > Reports > Students (Tab) > Birthdays report.
Enter a date range, and this report will display all students with a birthday in that given period, as well as the age they will be on their birthday.
If you want to check which students are going to be a certain age ( e.g. 5 years old), enter that figure in the New Age column and press return. This filters the report to display only those who will be 5 years in the period of time selected.
If you require a report that shows student ages in years and months, then go to Reporting > Reports > students (tab) > Date of Birth.
This report will give you the student name, year, form, address, birthday and current age in years, months and days.
If you require the students' UPN in a birth date or age report, you can go to Reporting > Custom Report
Select New Report. Then, on the right side, Dates tab, select Age in Years and Exact Age, then run the report.
You will automatically get student UPN, Name, Form, Year as well as columns for the Date of Birth, Exact Age and Age in Years.