There's a ratio that someone (Sue Donohue???) made up for the mediterranean tortoises. Maybe one of our members can give you the details. I can't seem to find it.
Search "Jackson Ratio"; it is a weight/length ratio, not a weight/age graph. At 5 y.o. it should be about 10-12 cm, but very often CB's can be even larger.
Here is a link to a Jackson's Ratio calculator that I use, which gives you more of an idea whether the length/weight ratio is healthy): http://www.tortoise-protection-group.org.uk/site/171.asp - if you need to convert inches to cm, just use Google for that (type e.g.: "5.5 inches in cm" and it should calculate for you - that's 14cm).
Our captive-bred 7-year-old Antakyan greek is 5.5 inches long and weighs 475g... he's on the small side for his species and age.
One of the little torts I rescued was 5.5 inches long and weighed 275g when I got him (Jackson's ratio of 0.10, which is severely underweight). My healthy 5.5 inch Russian tort weighs 500g (Jackson's ratio of 0.185 = healthy). Plugging those numbers into the Jackson's ratio calculator gives you an idea whether your tort is spot on, overweight, or underweight. There is an explanation of it under the calculator.
CactusVinnie said:
Search "Jackson Ratio"; it is a weight/length ratio, not a weight/age graph. At 5 y.o. it should be about 10-12 cm, but very often CB's can be even larger.