These tortoises are all above the 4" size, which the FDA suggests they need to be in order to be sold as pets, for kids. These tortoises are typically at least 1 year old (depending on the species, sometimes much older), and very well established.
For younger or baby tortoises, see the individual species categories or Click Here for a list (by buying smaller tortoises, you are buying for educational, scientific, export, or "from turtle fancier to turtle fancier," per the law).