'Boyhood', a soon-to-be-released movie is doing something that was never attempted by a major film before. Filmmaker Richard Linklater made a movie about growing up and decided it would be interesting to film it using the same actors for all stages of the story and therefore it took 12 years to complete. The youngest actor was 7 when filming started in 2002, and 19 years old when they finished.
To this point, production companies and filmmakers have always cast different actors at different ages to play the same character in his different stages of life (for obvious reasons, not the least of which it is much less costly and takes far less time to produce a finished product). No one has been willing to wait 5-15 years in order to film a scene or two, if they can find a talented and close-enough-looking actor who can play the younger/older-self of the main character.
What Richard Linklater decided to do with his latest film "Boyhood" is groundbreaking and unheard of. It is a huge commitment with so many risks most filmmakers won't even think of doing.
Check out the trailer of "Boyhood" starring Ethan Hawke, Ellar Coltrane and Patricia Arquette and see how they grow up in front of your eyes. That's some dedication and work ethic.