How old can a ghost be?

In the UK, it's not unusual for old buildings to have stories of ghost sightings. Pretty much any castle of note has a medieval ghost walking around as have most stately homes.

If you look at even older sites associated with the Romans, you'll hear claims of ghostly goings on, people seeing soldiers or hearing voices speaking Latin.

But that's about it, you never hear of anyone seeing ghosts from older than the Roman period. There's no iron age ghosts, no cavemen ghosts.

Why?
How old can a ghost be?
How old can a ghost be?
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