Depending on your definition 26 years
A portrait is an artwork or an artistic representation of a person. Its goal is to portray the personality, mood or the likeness of a certain person. A portrait usually shows the person looking at the painter or the artist for the goal of engaging the subject to the audience. A good example of a Roman portrait painting is the bust of Julius Caesar. Only two of his portraits survived through the years and the one is called the "Tusculum portrait".