How far in advance can I apply for Social Security retirement benefits? You can apply for Social Security retirement benefits when you are at least 61 years and 9 months of age. You should apply three months before you want your benefits to start. Even if you are not ready to retire, you still should sign up for Medicare three months before your 65th birthday. When you’re ready to apply for retirement benefits, use our online retirement application, the quickest, easiest, and most convenient way to apply. More Information. How To Apply Online For Social Security Retirement Benefits