If you've already reached full retirement age, you can choose to start receiving benefits before the month you apply. (ssa.gov)
No matter what your full retirement age (also called «normal retirement age») is, you may start receiving benefits as early as age 62 or as late as age 70. (ssa.gov)
And the reductions aren't small: Benefits are reduced by 30 % if you opt to start receiving benefits just five years early. (smartasset.com)