Biggest ATB I've seen is around 6feet long and as big around as a lemon... and colored like one too
All of the ones we have at outback are nippy, too... wild caught amazons will tend to do that. And I believe they go for the heat signature of our exhalations, hence the tendency for them to strike at faces.
I personally have a pair of captive bred babies, almost yearlings, that are fairly tame. They are around the 24 inch range i think (hard to accurately measure a skinny, squirmy red noodle). I am hopeful that they will stay this "tame" once they get large enough to hurt.
Nice yellow ATB waltah!