British television viewers have recently been subjected to a slightly creepy advertisement in which a ­digitally resurrected Audrey Hepburn eats chocolate in an open-topped car. The slightly reptilian movement of the figure is disturbing enough, as is the faux nostalgic 1950s setting. By contrast to this trickery, a few snaps of the remote control might summon up the “real” young Hepburn playing on another channel in Roman Holiday or Funny Face.Film has this ability to preserve youth, as fresh as the day it was captured on camera. Ageing is something that happens off-screen. Until now, when a film by the American director Richard Linklater follows a boy, Mason (Ellar Coltrane) from age six to 18, in real time. Boyhood was necessarily a long-term collaborative project. Link