It also could be genetic...
I rescued a small albino 50/50 cal king, the owner had gotten him as a near hatchling, 2+ yrs ago now, fed weekly, never escaped... Hardly grew an inch.
I gave him to a friend so see him often, he has shed, but not grown. Eats like a pig.
here is a pic of him soon after i got him.
The previous owner had pics dated back those two years.