Once you're eligible for Medicare, you'll have an Initial Enrollment Period to sign up. The Initial Enrollment Period starts 3 months before your 65th birthday and ends 3 months after. Make sure to terminate your Georgia Access coverage as soon as you enroll in Medicare.
If you are enrolled in Medicare Part A or Part C, or are eligible for premium-free Medicare Part A, you are considered to have another source of comprehensive coverage, and will not be eligible for premium tax credits through Georgia Access. In most cases, it's to your advantage to sign up for Medicare when you're first eligible. If you decide to keep your coverage through Georgia Access and you are entitled to Free Medicare Part A, you will have to pay full price. If you are paying a premium for Part A, you may drop your Part A and B coverage and get coverage through Georgia Access with subsidies, if eligible.
Visit Medicare.gov for more information about this program, including information about how to enroll.