When i got my snake she was no bigger then 14 or so inches and i put her right into a 55 gallon tank. I have a lot of stuff in the tank( several climbing logs, multiple hides, lots of vegetation and so on..

They say that if you put more stuff in the tank it will make the space seem smaller and make the snake more comfortable if they start to get stressed by the tank size

But never had a problem with her going off feed other then when she got sick. A lot of people say this is not a good thing but i got the tank for free so really couldn't beat the price and i figured it was something she would definitely grow into. And she is doing just that!