I don't have a lot of experience, but I did adopt a BP that was about 6 or 8 months older than mine. She weighed about 600 grams in relation to my younger male who weighed 574 at the time. She was a little longer, but definitely skinnier. I started feeding her on the same schedule as Alice and she filled out quite nicely. Now, six months later, she weighs 1110 (1326 before fast) and he weighs 1039 (1106 before fast). She caught up fast.

Robbin