Yes mine all cooked young and before they left primary there is no way they would have starved, they could do the compulsory spag Bol, noodles and easy stuff like scrambled egg, jacket potatoes in the microwave, and a full dinner by 12 plus cakes, biscuits etc (better than me mostly) I think it’s not so much the not cooking in this situation but the not cutting up that would worry me enormously
You can’t change his parents but you can make him more useful when he comes to yours most kids like experimenting and trying out doing new things