I agree 9 to 12 inches is a normal hatchling size for Cal kings, BUT, I have hatched individuals out at 15 inches. So it CAN be called a hatchling at that size.
Also adults are easily defined. They are adult when they become sexually mature, period. And that is from 24 inches, aprox(rarely smaller) up.
I have had 18 inch 10 month old males successfully sire offspring, so they have to be considered adult. Of course I have seen many two foot females successfully reproduce.
The actual size they become sexually mature is conditional, it really depends on support, both in nature and captivity.
The problem with reptiles is, they have genetic potential, with cal kings they have the potential to reach five feet or so. Yet, most individuals do not reach that. In fact, some individuals never exceed 30 inches in nature and in captivity. Yet, that are full on reproductive adults.
This is also controlled by regional genetics as well. While its possible to find a five foot western king in many different locals, most locals never see such a large western king. Anyway, thanks for your ear(eye) Cheers