Age requirements are all dependent on where you are riding your ATV in Georgia. Some parks offer special ATV trails for drivers without a license, while others will require you to be 16 years of age and have a valid driver's license. Also, since some towns may allow ATVs in public areas or on the road, you'll need to follow the law in accordance with each situation.
Check out these Buford, GA ATV/OHV resources:
