You may find this to be helpful. It’s part of the definition of Uniform Normal Retirement Age from the definition section of the 401(a)(4) regs. 1.401(a)(4)-12.
(4) Conversion of normal retirement age to normal retirement date. A group of employees does not fail to have a uniform normal retirement age merely because a defined benefit plan provides for the commencement of normal retirement benefits on different retirement dates for different employees if each employee's normal retirement date is determined on a reasonable basis with reference to an otherwise uniform normal retirement age and the difference between the normal retirement date and the uniform normal retirement age cannot exceed six months for any employee. Thus, for example, benefits under a plan do not fail to commence at a uniform normal retirement age of age 62 for purposes of § 1.401(a)(4)-3(b)(2)(i), merely because the plan's normal retirement date is defined as the last day of the plan yearnearest attainment of age 62.