When did this happen? Probably gradually about 2000 to 500 BC. Both Egyptian and Greek refer to iron in terms that indicate it came out of the sky, so the true iron age would have come after that.
As to the Punxsutawney site: it was probably in use for a long time. The iron smelting could be recent and some of the other artifacts very old. Shouldn't be a problem.
Okay, you can have the first bid on the Brooklyn Bridge replica.