Georgia Code § 3-3-23. Furnishing to, purchase of, or possession by persons under 21 years of age of alcoholic beverages.

Under this statute your son could face up to 6 months in jail and up to a $300 fine. These are all possibilities. However I draw your attention to the following section of law designed for first time offenders which it sounds like your son qualifies.

(c) Whenever any person who has not been previously convicted of any offense under this Code section or under any other law of the United States or this or any other state relating to alcoholic beverages pleads guilty to or is found guilty of a violation of paragraph (2) or (3) of subsection (a) of Code Section 3-3-23, the court, without entering a judgment of guilt and with the consent of such person, may defer further proceedings and place such person on probation upon such reasonable terms and conditions as the court may require. The terms of probation shall preferably be such as require the person to undergo a comprehensive rehabilitation program (including, if necessary, medical treatment), not to exceed three years, designed to acquaint such person with the ill effects of alcohol abuse and with knowledge of the gains and benefits which can be achieved by being a good member of society. Upon violation of a term or condition of probation, the court may enter an adjudication of guilt and proceed accordingly. Upon fulfillment of the terms and conditions of probation, the court shall discharge such person and dismiss the proceedings against him or her. Discharge and dismissal under this subsection shall be without court adjudication of guilt and shall not be deemed a conviction for purposes of this subsection or for purposes of disqualifications or disabilities imposed by law upon conviction of a crime. Discharge and dismissal under this subsection may occur only once with respect to any person.