I personally never go by weight when feeding BPs. I feed my snakes prey that roughly the exact same size as it's fattest part of the snake's body. I do not know if this makes a difference though.

200g for a three month old BP is actually quite a good size. I have 1 year olds that are barely 500g yet. I have a two month old that is 164g. I have been told that 500g gain per year is a good healthy weight gain until the BP is roughly 3 years old. Then their growth will slow down.

Many people do it differently. I do feed my ball pythons that are under 500g once every 5 days. Anything over that gets fed once every week. A ball python will be fine though (no matter the age) feeding once a week. A hatchling BP will not starve being fed once a week. This choice however is up to you.