As noted, "Gran Torino" has some weird similarities to the Pixar animated hit "Up." They are two of the top five grumpy-old-guy-meets-cute-kid movies.
"Up." (2009) Ed Asner is the voice of the grump; Jordan Nagai is the boy who stows away.
"Gran Torino" (2008) Clint Eastwood, Bee Vang.
"Bad News Bears." (1976) Walter Matthau, Tatum O'Neal.
"The Professional." (1994) The grumpy old man, played by Jean Reno, is a paid assassin; Natalie Portman is the adorable kid.
"Sling Blade." (1996) Billy Bob Thornton, Lucas Black.