Q. What is the difference between being vested in the retirement service and being eligible for a retirement benefit?
A. There isn’t any difference. To be vested in the retirement system, you must you must have at least 5 years of creditable civilian service. If you were to leave government after having 5 years of creditable service under your belt (and didn’t ask for a refund of your retirement contributions), you’d be entitled to an annuity at age 62.