Thats a perfectly fine size. They all grow at different rates. I have an adult three year old female who is 1350g and about 3 1/2 ft! Body state is much more important of a factor than the age of the snake. If the snake looks healthy, you're on the right track. It's okay for them to stop growing or platueu for a bit, and they might go through periods like that especially if they aren't feeding super well. Nothing to worry about imo!