Charts don't mean a thing
1# They grow at different rate
2# At such a young age it depends on the size out of the egg, how fast the animal started to eat, how big of a prey, and feeding frequency.
So can a 2 months old be in the 70's on empty? yes it can.
I have hatch BP anywhere from 40 grams to 95 grams out of the eggs, some will start eating after their first shed (10 days) some will take a few weeks.
Bottom line it should really be about overall look then a number.