I gave up a whole bunch of times. Really. The stupid piece of crap I was learning on was so anti-rideable that I several times threw it in the corner.
Picture:
http://www.unicycling.org/unicycling/Unidb/qdesc/troxel.html
But I kept coming back. What spurred me on was the knowledge that a totally ordinary human from my neighborhood could do it (and idle). If he could, why couldn’t I? It’s a good thing I never figured out, back then (age 14) that he had a Schwinn and I had a P.O.S. By comparison, the Schwinn was a Cadillac and a Hummer rolled into one.
But I eventually got it. Only then did my Troxel become almost completely unrideable, by falling apart under the weight of its rider.
I know people who can’t do lots of things. Including drive cars. I asked about that when I worked for the driving school. Does anyone ever not learn? The answer was along the lines of that there were people who shouldn’t ever drive. But for the most part, unless the person has brain damage, or lacks cognitive skills, or has physical damage keeping them from working the controls, they can learn if they work at it long enough. We had more than one student who took lessons for more than a year before passing a road test.
I still can’t juggle six balls with any regularity. But I have not failed. I will not fail, even if I never finish learning.
So the answer may be no. Some people are better tuned to their balance than others, but I believe if you have the physical and mental equipment, you can learn to ride if you stick with it. If you have neurological, inner ear, cognitive or other damage, this could impede or stop you though. But I also know of several people who have overcome all sorts of obstacles to ride, including people with varying levels of developmental disabilities (retardedness), learning disabilities, bone problems, and blindness.
Better examples are given by places like the St. Helens school in the 60s and 70s when all the kids were riding unicycles. Did every kid in school ride? According to what people tell me, no. It was not a requirement of PE, to my knowledge. But the vast majority of the school’s population rode. This works well as a (small) population sample.