Excellent question! Thank you so much for asking me 😀 This is one of my favorite things to discuss with my friends. The short answer is as you guessed, it depends.
To me traditional witchcraft means a folk magical and spiritual practice handed down for multiple generations. To some traditional means not-wiccan. (From my definition, Wicca is traditional witchcraft, from the other definition, Wicca is the definition of what is not!)
It can be further narrowed down or it can be expanded in meaning.
How is it handed down? Some would say it has to be orally and/or directly by living people. Others would say reading of old practices is sufficient. Even others would direct you to practices handed down by the dead or by fairies or other spirits. If you go by the book or spirits or past life definitions, the age of the tradition could be timeless! One could without much trouble follow biblical folk magic as described from as early as Genesis or old Greek Magic from the Magical Papyri both are multiple thousands of years old!
How much can it be changed and still be traditional? Most lineages of traditional witchcraft have many changes to them from the older generation. Many forms of witchcraft were just barely polytheist or pagan before the 19th and 20th centuries. But both the pagan revivals in the 19th century and the Witchcraft revival in the 20th century added polytheism to many older forms of folk magic.
The definition can be even further narrowed down to insist that the previous generation of practitioners called themselves witches or some equivalent, or that their neighbors called them that. Others use witch as a modern term to describe cunning folk, trade guild folk magicians, folk magic midwives, pellars, fortune tellers, wort cunners, fairy doctors, and/or root doctors and so on.
How far back is going to vary greatly depending on the tradition. I find the Saveok Water Archaeology Witch Pit discoveries as very convincing evidence of a consistent folk magical tradition going back to the 16th century in one location. However, no one will talk about it except in passing to say there were rumors the residents were witches.
We could keep on going with narrowing or expanding the age based on the definition. I will simply say, the age of traditional witchcraft is entirely dependent on your definitions of traditional and of witchcraft. By my definition, witchcraft is pre-historic and that the majority of the traditions we follow today at the oldest are reconstructed from ancient times or are handed down directly less than a thousand years and probably more like an average of 300 years.
The clincher is, the vast majority of those oral traditions handed down within the last couple hundred to a thousand years, are secretive and do not want to come out. You can find archaeological traces of them, historical records that seem to follow a similar theme and folkloric studies about them, but many of the trails grow cold due to tight lips.