In Looper, Joseph Gordon Levitt plays a young version of Bruce Willis's character, Joe. In order to make Levitt look more like Willis, the makeup artists applied heavy prosthetic makeup to his face. This included adding wrinkles and age spots, as well as changing the shape of his nose and mouth. The result was an incredibly realistic transformation that helped sell the movie's premise that two different actors were playing the same character at different points in his life.
While some may have found the makeup distracting, it was undoubtedly effective in making Looper a visually unique film. It's also worth noting that Gordon Levitt is no stranger to wearing heavy makeup in movies; he previously donned prosthetics for his role as John Blake in The Dark Knight Rises. So if anyone is up for the challenge of convincingly transforming into another actor, it's definitely him!