I don't know. Since the series will probably span over several decades if not centuries in the case where the show creators want to depict all the main events of the second age (The crafting of the rings of power, War between Sauron and the Elves in Eregion, Numenorean imperaliasm, Sauron bending the knee to Pharazon...), I think they will more likely pick up an actor in his thirties or forties for the role of Ar-Pharazon and age him over the course of the series (just like they did for Travis Fimmel in Vikings).