The exception applies if your separation from service with the employer that provides this plan occurs at *any* time during (as in your case) or after the year in which you reach age 55.
The plan administrator *should* report this with code 2 in box 7 of the Form 1099-R since they know your birthdate and separation date. If they do report it with code 2, you won't need to file Form 5329 to explicitly claim the age 55 penalty exception. If the plan administrator instead uses code 1, you 2017 tax return will need to include Form 5329 to claim the exception.
