Depends. I have one of the smallest species of garter snakes. They grow extremely slowly. My 8 month old ones just hit 9 inches. My 1 year old hit 13 inches 3 weeks ago. When they were born, they were two and a half inches long, the runt was two inches and Pumpkin was 3.5 inches. He's also the best eater and the fattest baby. They were born on March 5th. I'd say they're growing pretty well. Yours looks a lot older than mine. At least, on your avatar it looks to be about the size of my 1 year old, Runt.