The Air Force starts providing retirement benefits after 20 years of service, no matter what age the person is. There is not a set age requirement since it depends on how old the person was when enlisting.
All Air Force members who wait the full 20 years are eligible for complete retirement benefits. These benefits do not require deducting payments from their payroll checks. Active duty U.S. Air Force members have the option of signing up for the Thrift Savings Plan or a 401(k) plan to put away more money for retirement. The member can withdraw the TSP and 401(k) funds from his retirement account at any age, even if he hasn't yet reached 20 years of service. However, the 401(k) plan may have penalties for early withdrawal.