Well, IMO the color change is age and not size dependent, so hard to use as prediction. First thing about size is to check if it's a true P. adspersus. You could check the odontoids and confirm it; but from looking at all posted pictures, it appears one.
Second thing would be it's genes; if it comes from a large male and mama was a huge female... then things are looking better. Unless you know breeders and line; impossible to tell. I even have theory why there has been no babies from selective line breedings reinforcing size to produce 10-12 in. males.
Third is that the baby/juvenile was given all the best care (right temps, clean water, best food) for those genes to manifest during juvenile stage... I know you did

. Think you have a good chance getting this guy huge.