Wondering uif anyone knows when Carin Terriers stop growing? at what age....

Small dogs usually stop growing between 12 and 18 months, and will often fill out until 2 years. My PRT was spayed very, very early, and did not stop growing until after she was 3. 

My cairn was full grown at one year of age.  The color of his fur has gradually changed from when he was younger.  He is nine now and almost solid black.  As a pup and young dog he was brindle. 

Well, I'm not sure when any dog stops growing.  I generally go by what the genetics say how big your dog is supposed to get, but cairen terriers don't get big, that's for sure, so he should be full grown definitely by 8 mos.  Misty's 6 mos. and everyone tells me she shouldn't get any bigger, just get more substance to her, not taller.  So, I hope they're right! 

By the way your pup is cute!  I used to have one when I was young, and he was the greatest little dog in the world.  He wasn't trained, but he knew his tricks and was just a terrific dog all around!  I loved him so much!