At 81 you don't want to be wrestling with a professional grade floor sander!!! They're brutes, and will destroy your floor in a heartbeat if you don't know how to use them properly.
Art is spot on; hire a professional. As a contractor I would never have tried to attack a client's floor myself. The risk of having an unhappy client, and having to replace the floor at my own expense, gave me sober second thought whenever I was tempted to rent a machine. Also, having seen the crappy results others have achieved by DIY reassured me in getting a qualified subtrade to do it. I've never seen an amateur job done that I would have accepted for a client.
Sorry, but that's the harsh reality.