how to group based on age in crystal reports

Question

hello everyone..

 

 

i have doubt in crystal reports...in my database i have three columns named age ,date of birth , name

ex:24 24/01/1991 abc

      28 25/07/1988 def

      5    28/03/2010 ghi

 

now in crystal reports i have to group it by above 21 and below 21...how to do that and next year age will change at that time also formula should work properly..i mean if i change dateofbirth...age should change and grouping should done perfectly ..how to do this...which formula have to use...any help