Here are three pictures to show hatchlings, an 8 month old, and at 13 months.
You should expect growth in this range depending on the enclosure and the genetics of your tortoise. I've seen yearlings much larger and much smaller than mine.
Last picture is a 16month old near her mama
Because they all grow at their own pace and depending on their food, how they were started, how they are housed now, there is no way of knowing if yours is too small or too big. If you have the temps, humidity, diet and exercise correct, the. He is growing the best s/he can
It would help if we knew his weight in grams. You can get a gram scale at Sears, Target or Walmart.
If your baby was started dry, which is typical, they often grow very slowly at first. Follow the care sheet on the sulcata page and they will usually turn around.