I think I bought mine when she was about six to seven months old, and she weighed around 16 grams. From there, she grew about six grams a month for a few months. She slowed down a bit after she passed 35 grams and started to fluctuate quite a bit. I didn't keep good records once she was nearing adult weight in the upper 30's. I'd guess that she was then growing a gram or two a month, but again, she'd sometimes drop a couple of grams over some period. Once she hit the 40's, she would go up and down a couple of grams on a regular basis.
Cresteds grow a bit faster if they are given crickets a couple of times a week along with your cgd. Just be sure the crickets are the right size for the gecko.