Standards, whites, beiges are usually fully grown at 8 months old. Black velvets, violets, sapphires
grow slower and can take well over a year and 1/2 to reach full size.
Yes, it does vary from color to color and from breeder to breeder and because of heritage, type of food, supplements, illness, fighting between siblings, richness (or the lack of it) in the mother's milk and in it's surroundings.
The proper care of the mom while she is developing is extremely important ... this is where the kits get their start in life. If she is not healthy or not being taken good care of ... it is also affecting the kits that are developing inside her.
When nursing, IF the kits are not getting sufficient milk and nourishment from the milk, this can stunt their growth.
Once a kit is weaned, continuing to give it high grade food and supplements will often determine size, also.
But, it has to have a good start to even have a chance to be a good-sized healthy chinchilla.
The first 6 months to a year are a chin's 'building blocks' on life. This will usually determine what condition (size, health) it will be in for life.
Ebonies, violets and sapphires are usually the smallest boned of all the colors.
Pure standard grays are the original color of all chinchillas and are have the potential to be the largest ... as a general rule.
The word "adults" takes in allot ...
and when are they considered adults
Adults, as in old enough to breed ... that depends on size as well as age ... and will vary from color to color.
Adults, as in as big as it will get ... you can make it continue to put on weight ... but ... this is not always a healthy thing for chinchillas. Over weight chinchillas are like over weight humans ... not healthy.
Some people/breeders 'consider' 6 months full grown, yet other people/breeders may say 12/18 months ... depends on who you talk to.
I do not consider a female chin an adult or put them into breeding until they are 1 year to 18 months old ... depending on the mutation color ... BUT ... that is just the guide line some of us follow ... I know others that but them into breeding much sooner. Who's to say who is right and who is wrong? The continued health of the line determines that.
To each his own ...
Jo Ann