I don't think there is any set "rule" on how fast or slow they grow. As long as the husbandry is spot on and they are eating regularly, they will grow at their own rate.

We got Autumn on July 11, she was about 4-6 weeks old 75g, and Jasper we got on August 6, he was about 6 months old at 230g. I started weighing them about once a month, to make sure they are getting an appropriately sized feeder and track their progress, but going forward we will probably only weight them after the shed & poop: