Twins that stay completely indistinguishable for their entire lives.
In fiction, identical twins will usually be shown looking exactly alike for their entire lives. This is usually necessary because the plot will make use of the fact that others cannot tell the two siblings apart. Any show or film in which two twins are played by the same actor will fulfill this trope, especially if the actor is an older person. In Real Life, twins start off life looking identical. However, as they grow older, their appearances tend to diverge due to differences in health, living environment, and lifestyles. For example, if one twin eats healthy and the other does not, they will end up looking different. Genetics is not the only thing that determines one's appearance.