It came about in the mid 20th century, authored as such by Gerald Gardner. I believe that was around 1950. However, that does not mean that contemporary Neo-Paganism or even Wiccan tradition is not much older.
Wicca is a form of religious witchcraft, and there is evidence that at least some of these practices are much, much older.
Some wish to claim that as Wicca is only around 60 or 70 years old, that it is invalid, somehow with the misguided belief that antiquity lends authenticity.
The truth is that Gerald Gardner may have founded Wicca, but religious forms of Paganism have existed for quite some time.
Gleb Botkin started the Church of Aphrodite on Long Island in 1938, some family traditions have been in existence for quite some time. In some families, these were syncretized with other religions.
Also, there are many newer denominations of Christianity coming about quite often, and many of them change over time.
So, while officially, Wicca is only some 60 years old in name, the traditions that comprise it are actually older than the religion itself.