I found this little snippet on stackoverflow
All credit goes to ScArcher2
This is a strange way to do it, but if you format the date to yyyymmdd and subtract the date of birth from the current date then drop the last 4 digits you've got the age :)
I don't know C#, but i believe this will work in any language.
20080814 - 19800703 = 280111
drop the last 4 digits = 28
This is just a great little snippet of code, and as an upside, dates in that format are easily sortable by standard numerical sorting methods (read: fast).