The ones I have are late 19th century. I would be just guessing the age. There are patents out there on different styles of irons but I think yours is allot older. Soldering has been around for over 5000 years.
Sep 22, 1327 - Then, on the night of September 22, 1327, his jailers prepared a fire and placed a plumber's soldering iron in it until it was red hot. Edward was held down, a cushion was placed over his head and the soldering iron was pushed up his anus, or as one chronicler ...
From Queen Isabella, the She-Wolf of France: Revenge on an Unfaithful … - Related web pages
http://www.suite101.com/content/queen-isabella-the-shewolf-of-france-a182407