Just a guess, but I would say that he should easily take down weaned rats and quite possibly "small" small rats too.

One of my girls is now almost 7 months old, is at 598g, and takes down small rats no problem. I have another girl who is 8 months old, is hanging tight at 465g, and takes down small rats also. Just one month ago they weighed the same, and got the same sized rats on the same feeding days between then and now. They just put on weight at different rates and have different "body types". It's the smaller, older girl that is actually more "fluffy" and the larger, younger girl that is solid as a rock.

Eric

Side note: a gram scale is a useful tool to have around - either a good kitchen scale or one meant for your collection only (my wife made sure I had my own ).