Oy, I tried some of the stuff on the ball. I can't do any of it. Well, I can lay prone over the ball and balance with one hand out and the opposite leg out, for about 3 seconds. Kneeling on the ball? I don't see how I could ever do this.
I know I have horrible balance, always have; it's not a function of age. I never thought I had a weak core, as I can do lots of crunch type stuff on the ball, but nothing with balance in any position, with or without the ball.
It's amazing I can even ride, when I think of it. I didn't learn until I was 10 and I remember one time finding myself drifting across a street and running into a parked car, with no control over what was happening. I still get that feeling in the beginning of a ride, especially if it involves a downhill.