I don't know about the usual growth rate because our boy was neglected before we got him. At what was said to be 6.5 months in the beginning of January when we took him in, he was 11 grams. At that point I truly believe he was at death's door. After a 2 week treatment at the vet's he came back to us at 14 grams. During treatment his food was being limited to about 6 bugs twice a day, mostly meal worms with some crickets. Watching him eat now, I don't think that was adequate either.
Since then he is a totally different dragon. He is a pig when it comes to eating bugs, as he should be. He loves BSFL and dubia roaches, although he gets 3-4 meal worms to help lure him to his salad dish. The others are not currently luring him to salad, but it is taking less meal worms to get him there over time, and he does eat at least a couple salad bites a day. Much better than when the meal worms were the only food he was offered. At his last weigh in on Friday, he was at 148 grams.
One thing I did that helped me feel better about Sir Henry's growth was to keep a weight chart. We weigh on Monday and Friday. It is nice to be able to see progress over time, and I know that if he does get sick and I have to take him to the vet, that information will be a help to them when it comes to diagnosing any problems he may have.