The movie is based on a story by F. Scott Fitzgerald, which postulates that a person could be born elderly, then get younger as time passes. That, in turn, had been inspired by a remark from Mark Twain, with echoes reportedly back to Greek mythology (unspecified - anyone know?).
Other relevant items - Bob Dylan's lyric "I was so much older then, I'm younger than that now," and Merlin's backward aging in The Sword and The Stone.
I'll close with this poignant excerpt found by Shaun Inman in Kurt Vonnegut's Slaughterhouse Five:
"When the bombers got back to their base, the steel cylinders were taken from the racks and shipped back to the United States of America, where factories were operating day and night, dismantling the cylinders, separating the dangerous contents into minerals. Touchingly, it was mainly women who did this work. The minerals were then shipped to specialists in remote areas. It was their business to put them into the ground, to hide them cleverly, so they would never hurt anybody again."
Now, before you move on to the half-shorn sheep and the belligerent 'roo, watch the trailer ; it's less than 2 minutes long and worth that much of your time (click on 480P, 720P, 1080P depending on the size your computer can handle - bigger is better)