There are indeed age ratings for Replay TV, yes. See, normal TV viewing uses the Watershed (9pm to 6am) to help prevent children from being exposed to age-inappropriate content.
But Replay TV content is available 24/7, which means the programmes aired between 9pm and 6am are too. That’s why age ratings are applied: to ensure that content is labelled for the minimum age group for which it is suitable. You can block content based on the rating with a special PIN code. To learn how to set up the parental controls and PIN code, just click here.