As MindyB says, this exception only applies if the 401(k) from which you took the distribution was with the employer from which you separated from service in or after the year you reached age 55. It does not apply to a distribution from a 401(k) at an employer from which you separated from service before that year.
Normally a plan would know your birthdate and separation date, and would use code 2 on the Form 1099-R to indicate that an exception applied. In that case you would not have to explicitly claim the exception, TurboTax would automatically treat the distribution as exempt from the early-distribution penalty. (Of course if the distribution was after age 59½, the Form 1099-R should have code 7 and there would be no penalty.)
