I'm in my 50's and have been wanting a Onewheel since they came out. Finally got a OW+, and was far too exuberant and immediately slammed myself into the pavement. Pretty bad road rash, an very sore wrist, and a nice gash on my elbow. I've now stopped trying to carve like a pro and am concentrating on building the right instincts and technique for safety. Wearing all the right protective gear (was wearing helmet and wrist guards before). Changed my settings to get the front of the board angled slightly up which has helped tremendously - gives me an extra inch of margin before the nose digs in and throws me thirty feet. :) I'm keeping my speed low too.
Bottom line this is inherently dangerous in many ways, but that can be minimized if I use my common sense and think about what that concrete felt like when I was thrown off the board.