For example, in Jumper (2008), David and Millie appeared as high school age kids and later as 20-something young adults, each played by two different actors. I believed that Max Thieriot would grow up to be Hayden Christensen, and that AnnaSophia Robb would grow up to be Rachel Bilson.
What are your favorite examples of good casting of young actors and older actors playing the same character?