That's on the small side. I have a group that will be one year old in the next week or so. Smallest is 655 grams and the largest is 1018 grams. Mine are probably a little bigger than average.
Want to go over your housing, hydration and feeding regime?
Tom, I have obsessively been reading your posts on sulcata care
He is living in a 40 gallon tank with organic top soil and cypress mulch. Basking is about 95 to 100. Cool side 80 to 85. Soak every other day. Calcium bone in tank. Outside two hours a day on weekdays, over six on weekends. Gass diet with weed treats. Recently achieved 90% humidity on cool side.
I got him about two weeks ago from a friend who was not taking care of him properly. He has pyramiding already and was bit by a dog about two to three months ago. He previously was raised on spring mix, very little sun, and no humidity.
I think humidity is a big factor. I've been raising mine with out humidity without knowing they needed it and my are about a year old and only weigh about 76 grams. I recently got the humidity up and started them on a more variety diet and they are gaining weight daily now. Plus they look a little happier.