Just a little additional insight; that's not really applicable in this case. The age 55 is 'within the calendar year' the participant turns 55 and not necessarily the actual age. For instance, the participant can terminate employment on January 1, 2018 while not turning age 55 until December 31, 2018 and still get exempted from the 10% excise penalty.
The same is NOT true for the age 59-1/2 distribution. In that case, you must actually reach the date which is 6 months after your 59th birthday.
Good Luck!