YEARFRAC « Date Time functions « Microsoft Office Excel 2007 Tutorial

15.19.1.YEARFRAC(start_date,end_date,basis) returns the year fraction representing the number of whole days between start_date and end_date
15.19.2.Use the YEARFRAC function to calculate the number of years between two dates.
15.19.3.Return the age of the person whose date of birth you enter into cell A1