Although the horse, Casey's Shadow, ages several years, the boy, Casey, does not age much at all.
When Buddy has cooked supper, can't find any plates, and is ranting about not being able to put dinner on the table with no plates, Lloyd is sitting in an armchair with Casey sitting on its arm as Lloyd tries to get him to read the words "the child" from the open book Lloyd is holding. At 0:18:08, Lloyd snaps the book closed in his left hand and puts his right hand to his face, but at 0:18:09 when the scene cuts to a closer shot of Casey and Lloyd for Casey's line "Randy put 'em in the bathtub", Lloyd has the book open on his knee.
The audio of the horse hooves hitting the dirt frequently does not match what the actual hooves are doing while galloping.