The best age to retire under FERS (Federal Employees Retirement System) depends on a few factors, such as your years of service and the type of retirement benefit you are eligible for. Generally speaking, if you have at least 20 years of creditable service, you can retire with an immediate annuity at any age. If you have between 5 and 19 years of creditable service, then the minimum retirement age is 55. However, if you wait until 62 or later to retire with fewer than 20 years of creditable service, then your annuity will be increased by 8% per year for each year that you delay retiring beyond the minimum retirement age.