Multiple reports in ASAP allow you to select the Birthdate as a field in the results set (Student Report, Class Roster, etc.). If you push the results to Excel, you can insert a new column next to the Birthdate and calculate the age.
Here is the formula:
As in =(now()-F4)/365, where F4 is the birthdate field for the student record.
Keep in mind, since you're running the report "today", the age calculation is only for "today". Be sure to print out a hardcopy or save a pdf version of the report to retain a copy for your files. When you save the Excel file and reopen the document - let's say a month later, the age will recalculate.