Even longer ago I saw the production of the BAC 1-111. The wing skins were made in just that way, too...starting with large billets of aluminium alloy and machined away to form the structure, then they were shot peened until the required curve was obtained.
Apparently the 1-11 skins were originally intended to be "chemically milled," which was theoretically a much cheaper process. This approach had to be discarded in practice, as witnessed above.