Here are a few photos of the earliest surviving Icons of the Apostles Peter and Paul. They’re from St. Thecla’s catacomb in Rome, and date from the latter half of the fourth century. Although older depictions of the Apostles survive, they are usually part of a narrative scene; these are the oldest surviving Icons of the Apostles in portrait.
As can be seen, the representations we have today of the two Holy Apostles in iconography date back at least 1600 years. This lends greater credence to the belief that the Icons we have of the Holy Apostles are indeed based upon their actual earthly appearance, as well as being stylized, symbolic representations.
Icon of Saint Paul
Icon of Saint Peter