I had to look but hex head bolts can date back to about 1840. I thought it was later then that. With machine cut threads and the condition I'm guessing not as old as it appears. As cannonmn suggested -any signs of modern welds?
I won't be wronged. I won't be insulted. I won't be laid a-hand on. I don't do these things to other people, and I require the same from them.
― John Wayne "The Shootist"