Just for starters, it seems to me that they double in size the first week or so. I am not exaggerating! Based on what I recall from Storey's Guide and my own runners, they hit almost adult size between 3 and 4 months, up in the 90%s by around 7 months. So the initial growth rate is (seemed to me, anyway) astronomical, slowing down at around 3 to 4 months as their bodies shift energies into developing into sexual maturity and getting ready for breeding.
Would love to read some statistics from someone on this.