If The Date Is August 27, 2008 And You Want To Quickly Calculate Whether Or Not A Person Is 21 Years Old, Would That Person Have To Have Been Born By August 27, 1987?
I just got a new job and will be required to check student IDs to determine if they are 21 years old, in order to sell them beer or liquor. I must be able to determine this very quickly and worried that I’ll get nervous and calculate incorrectly.

