At what age the brain of a child develop enough so that he can take any decision ?

Varies with definitn: The brain continues to mature and make connections that finalize thinking until into the 20's. Women a little sooner than men. Infants are taught by parents example that they are little kings/queens who provide all their needs with a simple cry. For some reason some adults think they will become well behaved suddenly after they learn to walk/talk. They don't. Right/wrong is crude until at least 8.