How is the adult Voldemort like the young tom riddle?

In the film version of Harry Potter and the Half-Blood Prince, Tom Riddle was played by Hero Fiennes-Tiffin at age eleven and Frank Dillane at age sixteen. Michael Berendt was also cast to portray Tom at age eighteen, but his scenes were cut from the final version of the film. The older more transformed Voldemort is portrayed by Hero's uncle, Ralph Fiennes.