I had this 20" unicycle for a while, which I’d bought at a garage sale
for a few dollars.
I’ve been trying it for about 10-15 minutes at a time on our very short
front patio where I could reach the wall on one side, and the railing
on the other.
Yesterday a neighbor saw me struggling that way and suggested that I
should try it out in the open. He said that he knew how to unicycle and
demonstared his skill after using my shoulder as a mounting support.
Cool! 
After he left I decided to use a different method. I used the overhung
branches of a tree to mount. The great thing about this is that my arms
could start in an already balancing position. The result was phenomenal
(for me that is) I could ride a few pedal strokes at first and
eventually managed to ride 45 meters within 15 minutes! I was so happy!
I was jumping up and down.
If my earlier struggles helped, my total training must have been about
an hour and a half. I ride my mountain bike two to three times a week
and can stand on it at red lights. That skill must have helped too.
I want to get a new unicycle now. I am thinking about getting a 24"
because I am 5’11 with an inseam of 34 with shoes. Is that a good size?
Should I go even larger? I would love to get a mountain unicycle but
they are more costly. What would you recommend?
Ali
P.S. I love this midlife crisis! You get to learn lots of great stuff!
:o)