So the myth is true! Tank size can permanently stunt a RES growth.
I'm not totally serious though- no idea on the long-term effects of growth stunting. But I got Mello when I was 6 years old and didn't learn about good turtle keeping until much, much later. I kept her in a 10 gallon until she was something like 10 years old- but by then, she's already at the size that she is now: 5 inches! I also know a girl who has a 12 year old RES that is permanently 5 inches too, for probably the same reason as me.
So some photos of this currently 16 year old, 5 inch kid.
I also updated to a very powerful filter a few months back. Her tank water is now permanently crystal clear.
turtle butt
Just for kicks, this is my 55 gal aquarium from last year (no turtles in here). I recently revamped the aquascape, so waiting for it to become lush before photos.