Qoute directly from DMV's website:

Your Virginia driver's license normally expires on your birthday and will expire when you reach an age that is divisible by five - 20, 25, 30, 35, etc. When you renew your license, it normally will be valid for five years. You may renew your driver's license as early as two years prior to the expiration date on your license. If you were convicted of two or more moving violations (one or more if under age 21) since your license was last issued, you must retake the two-part knowledge exam and any other knowledge exams for each type of license you hold.