Layers should get about 1/4lb of feed daily...
I feed my layers that amount split into a morning and afternoon feeding, I feed broilers on the se schedule they just get more
Even on layer feed if that was a CX it would be the size of a small turkey. 16% is still plenty for them to gain weight, it would be slower but not that slow.
To the OP.... How much feed does it eat? If it was a CX it would live by the dish, and eat 5 times as much food as your other birds...
I don't think that's a CX....
20 weeks old, even on a restricted diet it would be well over 10lbs.
Notice how tall it is, Cornish cross are not that tall, also look at the legs even young CX have super think legs and that are shorter.
It's a pretty pullet, maybe a white rock?