My tortoise is around 1 1/5 years old and I am wondering if he is to small for how long he has been alive. He is a sulcata tortoise. I don't know how much he weighs. Here is a picture of him.
They all grow at different rates and there are a wide variety of factors that determine growth rate. Your tortoise is on the smaller side, but still well within "normal". Nothing to worry about at all. I would not even think about size and growth, but instead concentrate on a good weedy, grassy, high calcium diet, good temperatures, good hydration, sunshine whenever weather permits, and lots of exercise in a well designed, big, safe enclosure.
These things will give you good health. With good health, the size will come.