There's really no scale to go by. Sulcatas grow at different rates. Some of our members have 4 year old sulcatas in the 30lb range and others have 4 year olds at about 10 lbs. You mainly want healthy tortoises, and the size takes care of its own as they mature.
In his book, The Crying Tortoise, Devaus says that at 1 year a wild sulcata is normally about 1kg. When 2 yrs old - may be 3kg. and after 3 years - 6 kg. (17lbs). At that time they start excavating their own burrows and aren't as likely to be found in small groups. That surprises me, as that seems quite fast growth for a wild sulcata, but he has done more to research wild sulcatas than anyone!
Certainly a sulcata kept in "monsoon" style closed chambers can grow even quicker than that. I know when I was purposely "slow growing" my sulcatas in an effort to reduce pyramiding (as was thought back them) I had sulcatas that were about 7-8 lbs at 3 years. Didn't help pyramiding at all, and now I see much more active and robust 2-3 yr olds letting them grow faster and more in line with what Devaux cites.
Because there are so many variables in how they are started, housed, fed, and grown, there really is no "normal". I've seen 3year olds that were 40+ pounds and 6 year olds that were barely 300 grams.
I subscribe to Yvonne's suggestion. Don't worry about their size. Just work to make them as healthy as possible. Good diet and hydration, lots of space, warm temps day and night, good UV in your winters and sunshine in the warmer months, etc…
Thank you both. I was just concerned with there weight compared to size or age. I am sure I can fatten them up. I have plenty weeds and grass that grows in my yards, if only spring would get here!