yes, the top does adjust and come off by spinning. As for grandma's age, I'm really not sure because I never met her, this is my MOM'S grandmother, and my mom is in her late 50s. Mom says that her grandmother had this stool "for as far back as she can remember".
Now, I don't know all that much - but to me, the condition seems to be "fair" at best. You can see that the seat has been cracked practically in half and repaired. The legs have been re-glued using that gooky old wood glue stuff. And the metal feet of the legs are pretty loose. It's great for decor, but I wouldn't sit on it for sure. Then again - perhaps I'm overlooking the fact that this thing could be well over a hundred years old.