I watch a lot of these old time movies and also I noticed the same thing on the show Petticoat Junction.
These movies have the pilots flying an old airplane, they have two levels of wings. One on top one on the bottom
Here is a picture of the type of plane
Two Wingged Plane
I also notice in these movies and on Petticoat Junction they always have two seats. One in front and one in back. BUT the pilot when he’s alone is always flying the plane from the back seat. BUT when there is a passenger the pilot is in the front seat flying it and the passenger is in the back seat.
My question is this, is there are reason for this? Or is it just something they do in TV and movies for whatever reason, like it’s easier to film that way.
Those are generally referred to as biplanes and the seating requirements vary by the model of plane but the one you describe is most common. It is done that way mainly because of weight and balance issues. You can’t just randomly put weight wherever you want on small planes. It affects the flying characteristics and can be a fatal issue if wight and balance are too far out of bounds.
Yes. It drives from consideration of what’s known as weight and balance.
In some small aircraft (including some biplanes) the front seat is well forward of the desired center of mass (commonly refereed to as the CG, or center of gravity). If a single person were to attempt flight while sitting there, the CM during flight would be forward of safe limits, and the plane’s fore-and-aft balance would be unacceptable (the plane’s minimum speed for decent control would likely be well above what’s safe).
A single person sitting in the aft seat is much closer to the desired CM, and thus the plane ends up with acceptable balance for safe flight. With two on board, the CM would be further forward than with one, but still within safe limits.
The Piper Cub is a common example of a plane for which this is true.
Here is a Wiki article on CG and weight and balance in case the OP wishes to read more.
And the reason the pilot flies from the front seat, when carrying a passenger, may be that when taxiing a tailwheel aircraft, especially from the rear seat, forward visibility is limited because the nose is sticking up in the air.