You can house a baby snake in an adult size enclosure, but if you do you have to make sure it is *heavily* planted and is basically packed full of hides, etc. They need to feel secure. The problem with this is that you probably won't get to see your snake very much, you will have a very difficult time finding the little guy for feeding and general maintenance as well. As well as enclosures like this as quite a task to maintain. But if you are willing to do all this, then there is no reason you can't house a baby snake in an adult sized enclosure... after all, in the wild snakes aren't combined to 2'x1' enclosures
As for enclosures influencing the size of the snake, this is an old wives tale... and this is why especially turtles are abondoned. Everyone assumes these cute baby turtles won't outgrow their small enclosures... but these animals will grow regardless! Its in their genes for the most part how big an animal will get