I don't think it's very old -- possibly 20 years or less. However, the glass shade MIGHT be "repurposed" from an old ceiling fixture ... or it could be original to the lamp. It's hard to tell from the photo.

Very much a 20th century (20s-50s), with a lot of the form of the standard wooden "club chair with loose cushions" but THOSE ARMS! I've never seen any like it, and I can't figure out what function they would serve with that shape. The wide spots are too far back to be "writing arms" and drinks would be endangered by the sitter's elbows ... perhaps it was a custom order for someone who needed the support for an invalid? Or liked to rest with their elbows sprawled out?

Yep, there it is. Good find, and it looks like Lindac92 pretty much nailed the date, too. And it's true, replacement shades, regardless of period, tend to be expensive... Those straps you spoke of... I suspect their purpose is merely to hold the socket body, which is probably a non-conductive plastic of some sort, on that white platform. I doubt very much that the metal straps have any part in conducting electrical current. That's what insulated wires are for. Could they act as a ground? Technically yes, but only to electrically bind all the metal pieces of the lamp together so that in the event there was a short circuit, probably caused by an insulation failure, the rogue current would be directed to the ground wire, which is always Green and which leads directly to the round pin of a three wire plug. I'm betting the lamp doesn't have a three-prong plug, or a three-wire cord. Regardless, if you're worried about it, get it checked out by someone who knows. Could be an electrician, but if you have a lamp repair shop anywhere nearby, take it there, have them address your electrical concerns and ask them to replace that missing screw (or whatever) while you're at it so that the bulb will be stable when you have it all together again, ready to use.

This was as close as I could find on ebay; presumably you've searched there? Perhaps this dealer could help you i.d. it. Antique-Onyx-Marble-Cloisonne-Table-Lamp This one popped up on pinterest, was listed on ebay for 149, but says it's out of stock. No way to know if it actually sold for that. Yours looks much finer than either of these examples. This dealer has many vintage lamps for sale. You might also contact them: https://www.ebay.com/usr/sunzza