Thats common sense. If they kept growing until they die of old age, there would be some very giant snakes out there.
I had a cal king that lived 35 years, hmmmmmmm he was almost four feet when obtained, He lived that 35 years after he was collected, he was collected as a hatchling. You get the picture, if he kept growing, how large would he be?
i work with wild diamondbacks colonies in nature, the old ones rattles narrow as they shrink up, like all old animals and us. They do not keep getting larger, they actually get smaller.
In the old days when that saying was coined, most reptiles were dwarfed to the max. So after a bunch of years of negleck, they were fed and grew a little.
I have mentioned before, I recieved one of the first albino Gophersnakes. It was seven years of age and two foot long. I fed the heck out of it and it grew to 4 1/2 feet. Which is far shy of what gophers could grow to. And it grew to that length in one summer.
Its not to say, a snake cannot grow later in life, but they surely do not keep growing after they reach their normal size. Again is so, there were be some very giant snakes out there. Cheers