I class an aduld as a 3year old plus, but it's also got a lot to do with size and weight if you intend on breeding. For example you wouldn't breed a female if less then 300 grams, but 350 would be better as a minimum (thats what i go off for a breeding female). for an average male i would say anything bigger then 4ft would be classed as an adult, and be on large mice, small-medium rats or a chick.