Birth Date - 18 or 21 Years Old

Is a customer of yours making a purchase with a minimum age limit, and you have to "Card" them? Find what day they must be born before, in order to make the purchase.

You are at least 18 years old if your birthdate is on or before: 3/20/2005

You are at least 21 years old if your birthdate is on or before: 3/20/2002