Depends largely on the child's size also. My boy was considered small sized and he could stand steadily by 6mths +. But my friend's boy is rather big sized and he only stood steadily at 14mths and only started walking without support at 17mths.
Also, they must be given the environment and opportunity to practise. Alot of kids are confined in small playpens that do not even require them to move around, why would they want to learn to move around in the first place?