Bottom line
A Reserve retirement takes 20 satisfactory years, and a year is satisfactory when you earn at least 50 retirement points in it. You normally draw retired pay at age 60, but qualifying active duty can pull that age down (never below 50). When you hit your 20 years, you submit a written request to move to the Retired Reserve Awaiting Pay list, and you submit it between 4 and 14 months before the date you want the transfer to take effect.
What it means for you
Whether you are on the Legacy Retirement System or the Blended Retirement System (BRS), the bar is the same: 20 good years, 50 points each. Track your points every anniversary year, because points cannot be moved between years to fix a short one. If you have done real active-duty time since 2008, check whether it lowers your retirement age. And when you are ready to start the clock toward pay, get the paperwork in inside that 4-to-14-month window.