Your PADI certification never expires; but if you haven't been diving in a while, it's better to be over-prepared than risk a problem because you forget something important. Dive shops also appreciate seeing a recent ReActivated date on your certification card.
ReActivate is the engaging, efficient way to refresh your scuba skills. In the first phase you will move quickly through topics you know well, then dive deeper on topics where your knowledge may have lapsed. Schedule optional in water practice with a dive professional and receive a new card that recognizes your new "ReActivated" date.