I juggled regularly in my 20's. Got to a point of respectability (or at least non-embarrassment) -- lots of 3 ball tricks, and comfortable with 4. A year ago I decided to pick it up again to energize dormant neurons and regain some movement symmetry. Alas, at first I could keep it going for about 40 times, then the next time 30, third time I'd drop after 20 tosses, etc. Unlike when I was learning and would improve at each go, now I got worse the more I did it.
So it seems I won't run off and join the circus after all (though it's tempting -- my wife directed circuses for 12 years .

Jon