Twelve calendar months commencing on January 1 and ending on December 31. in which you reach age 70½ (if born before July 1, 1949), age 72 (if born after June 30, 1949), or age 73 (if born after December 31, 1950). 
Internal Revenue Code 401(a)(9) requires you to begin receiving benefits before April 1 of the year following the calendar year Twelve calendar months commencing on January 1 and ending on December 31. in which you reach age 70½ (if born before July 1, 1949), age 72 (if born after June 30, 1949), or age 73 (if born after December 31, 1950).
If you become subject to the required minimum distribution rules and elect a lump-sum or any five-year option, at least a portion of your benefit is your required minimum distribution and cannot be rolled over. Should your elected distribution option result in a payment lower than the required minimum distribution amount, your benefit will be increased to satisfy required minimum distributions rules.