They shed at their own shedules and it becomes less with age and size.
At 19" he's probably close to full grown so he will shed less and you might want to consider transitioning him to the adult diet.
As their metabolism slows down they require less protein and too much is in fact bad for their health.
As for the age, my girl is now two months, weighs 15g and is around 7cm (snout to vent).
My boy was 350g and 23cm (snout to vent) at 8 to 9 months old.