What age should a toddler know how to share ??

We went to DH's aunts house today and Kimberley would not share a doll with his cousin's little girl after we kept telling her to share after a few minutes his aunt went up to Kimberley took the doll from her and she had hold of them tight and took them away. I know that is what you are meant to do with them but Kimberley then stood there and cried for ages.

All his aunt kept telling me is she needs to learn how to share because of Alex.
Part of me is angry because of what his aunt did. I am sure in time Kimberley will share but i am still not sure she really knows yet.