What are the oldest and wisest men in Rome called?

They had no particulat title that I'm aware of. An old man was a senex. If he were a sensible old man he would be senex sapiens, a wise or prudent old man, he was senex prudens, if he were an experienced old man he would be senex peritus. Out of the three connotations, senex prudens would be the most fitting term for a wise old man.