My Horsfield tortoise is just under 20 years old and measures 6 inches across his back from his tail to the front of his shell. I've read online that for his size he should weight around 900g to 1000g but he only weighs 523g. I feed him almost every day and most days. These days he's mostly been eating kale and dandelion leaves. I give him more than what i think he'll eat and he normally eats most of it and leaves just a little behind. He's been very active and there hasn't been any change in his behaviour.